The Nervous System. Introduction Organs of the nervous system are divided into the Central (CNS) and the Peripheral (PNS) nervous systems. These structures

The Nervous SystemThe Nervous System

IntroductionIntroduction

Organs of the nervous system are divided Organs of the nervous system are divided into the Central (CNS) and the Peripheral into the Central (CNS) and the Peripheral (PNS) nervous systems. These (PNS) nervous systems. These structures provide sensory, integrative, structures provide sensory, integrative, and motor functions. Nervous tissue and motor functions. Nervous tissue includes neurons, which are the includes neurons, which are the structural and functional units of the structural and functional units of the nervous system, and neuroglial cells.nervous system, and neuroglial cells.


1.1. Sensory FunctionsSensory Functions derive from derive from sensory receptors at the end of sensory receptors at the end of peripheral neurons. Receptors gather peripheral neurons. Receptors gather information by detecting changes inside information by detecting changes inside and outside the body and then convert and outside the body and then convert the info into nerve impulses, which are the info into nerve impulses, which are transmitted over peripheral nerves to transmitted over peripheral nerves to the CNS.the CNS.


2. 2. Integrative functionsIntegrative functions are receiving are receiving signals and bringing them together, signals and bringing them together, creating sensations, adding to memory, creating sensations, adding to memory, or helping to produce thoughts that or helping to produce thoughts that translate sensations into perceptions.translate sensations into perceptions.


3. 3. Motor functionsMotor functions employ peripheral employ peripheral neurons, which carry impulses from the neurons, which carry impulses from the CNS to responsive structures called CNS to responsive structures called effectors (muscles and glands that effectors (muscles and glands that secrete when stimulated).secrete when stimulated).

Neurons: Basic Unit of Neurons: Basic Unit of the Nervous Systemthe Nervous System

Neuron StructureNeuron Structure

Cell Body (Soma)– Cell Body (Soma)– consists of granular consists of granular cytoplasm, cell cytoplasm, cell membrane, membrane, organelles, and a organelles, and a network of fine network of fine threads called threads called neurofibrils, which neurofibrils, which extend into nerve extend into nerve fibersfibers


Nerve Fibers –Nerve Fibers – extend extend from the cell bodyfrom the cell body


Dendrites – oDendrites – one neuron ne neuron may have many may have many dendrites; short and dendrites; short and highly branched; highly branched; together with the together with the membrane, dendrites membrane, dendrites are the neuron’s main are the neuron’s main receptive surfaces with receptive surfaces with which fibers from other which fibers from other neurons communicateneurons communicate


Axons – Axons – one neuron has one neuron has only one axon; arises only one axon; arises from slight elevations of from slight elevations of the cell body; begins as the cell body; begins as a single fiber but may a single fiber but may give off side branches; give off side branches; near its end it may near its end it may have fine extensions have fine extensions that contact the that contact the receptive surfaces of receptive surfaces of other cellsother cells

Neuron StructureNeuron StructureSchwann cells – Schwann cells – neuroglial neuroglial

cells that enclose large cells that enclose large axons forming axons forming myelin myelin sheaths sheaths that wind tightly that wind tightly around the axon; portions around the axon; portions of the Schwann cells that of the Schwann cells that contain most of the contain most of the cytoplasm and the nuclei cytoplasm and the nuclei remain outside the myelin remain outside the myelin sheath and make up the sheath and make up the nuerilemmanuerilemma (neurilemmal (neurilemmal sheath); narrow gaps in the sheath); narrow gaps in the myelin sheath between myelin sheath between Schwann cells are called Schwann cells are called nodes of Ranviernodes of Ranvier


CNS – CNS – myelinated nerve fibers are also myelinated nerve fibers are also found in the central nervous system; found in the central nervous system; myelinated fibers appear white, and myelinated fibers appear white, and masses of such fibers form masses of such fibers form white white mattermatter in the CNS; unmyelinted nerve in the CNS; unmyelinted nerve fibers and neuron cell bodies form fibers and neuron cell bodies form gray gray mattermatter within the CNS within the CNS

Types of Neuron and Types of Neuron and Neuroglial Cells Neuroglial Cells

Classification of Neurons:Classification of Neurons:Structural DifferencesStructural Differences

Bipolar NeuronsBipolar Neurons – cell – cell body has two nerve body has two nerve fibers one arising fibers one arising from each end; from each end; one is an axon and one is an axon and the other is a the other is a dendrite; located dendrite; located within specialized within specialized

parts of the eye, parts of the eye, nose and earsnose and ears


Unipolar NeuronsUnipolar Neurons – – single single nerve fiber that extends nerve fiber that extends from the cell body then from the cell body then divides into two branches; divides into two branches; one connecting to a one connecting to a peripheral body part and peripheral body part and functioning as a dendrite, functioning as a dendrite, and the other entering the and the other entering the brain or spinal cord and brain or spinal cord and functioning as an axon; functioning as an axon; some cell bodies gather in some cell bodies gather in specialized masses of specialized masses of nervous tissue called nervous tissue called gangliaganglia(located outside (located outside the brain or spinal cord)the brain or spinal cord)


Multipolar NeuronsMultipolar Neurons – – have many nerve have many nerve fibers arising from fibers arising from their cell bodies; their cell bodies;

only one fiber is an only one fiber is an axon and the rest are axon and the rest are dendrites; neurons dendrites; neurons which lie within the which lie within the brain or spinal cordbrain or spinal cord

Classification of Neurons: Classification of Neurons: Functional Differences Functional Differences

Sensory NeuronsSensory Neurons (afferent neurons) – (afferent neurons) – carry impulses from peripheral body parts carry impulses from peripheral body parts into the brain or spinal cord; most are into the brain or spinal cord; most are unipolar, but some are bipolarunipolar, but some are bipolar

Classification of Neurons: Classification of Neurons: Functional DifferencesFunctional Differences

InterneuronsInterneurons (internuncial (internuncial oror association neurons) – association neurons) – lie within the lie within the brain and spinal cord; multipolar and link brain and spinal cord; multipolar and link other neurons; transmit impulses from other neurons; transmit impulses from one part of the brain or spinal cord to one part of the brain or spinal cord to another; direct incoming sensory another; direct incoming sensory impulses to appropriate parts for impulses to appropriate parts for processing and interpretingprocessing and interpreting

Classification of Neurons: Classification of Neurons: Functional DifferencesFunctional Differences

Motor NeuronsMotor Neurons (efferent neurons) – (efferent neurons) – multipolar and carry impulses out of the multipolar and carry impulses out of the brain or spinal cord to effectors; stimulate brain or spinal cord to effectors; stimulate muscles to contract or glands to secretemuscles to contract or glands to secrete

Classification of Classification of Neuroglial Cells: Neuroglial Cells:

Neuroglial cells fill spaces, provide structural Neuroglial cells fill spaces, provide structural frameworks, produce myelin, and carry on frameworks, produce myelin, and carry on phagocytosis. Within the PNS neuroglial phagocytosis. Within the PNS neuroglial cells include Schwann cells; in the CNS they cells include Schwann cells; in the CNS they greatly outnumber neurons and are of the greatly outnumber neurons and are of the following types:following types:

Classification of Classification of Neuroglial Cells:Neuroglial Cells:

Microglial CellsMicroglial Cells – – scattered scattered throughout; support throughout; support neurons and neurons and phagocytize phagocytize bacterial cells and bacterial cells and cellular debriscellular debris


AstrocytesAstrocytes – – found between found between neurons and blood vessels; neurons and blood vessels; provide structural support, provide structural support, join parts by numerous join parts by numerous cellular processes, help cellular processes, help regulate the concentrations regulate the concentrations of nutrients within tissue; of nutrients within tissue; form scar tissue that fills form scar tissue that fills spaces following injury to spaces following injury to the CNSthe CNS


Ependymal CellsEpendymal Cells – – form an epithelial form an epithelial like membrane that like membrane that covers specialized covers specialized brain parts and brain parts and forms the linings forms the linings that enclose spaces that enclose spaces within the brain and within the brain and spinal cordspinal cord

Cell Membrane PotentialCell Membrane Potential

A cell membrane is usually polarized as a A cell membrane is usually polarized as a result of unequal ion distribution.result of unequal ion distribution.


Distribution of IonsDistribution of Ions

a. a. Ion distribution is due to pores and Ion distribution is due to pores and channels in the membranes that allow channels in the membranes that allow passages ofpassages of some ions but not otherssome ions but not others

b. b. Potassium ions (K+) pass more easily Potassium ions (K+) pass more easily through cell membranes than do Sodium through cell membranes than do Sodium ions (Na+)ions (Na+)


Resting PotentialResting Potentiala. a. a high concentration of sodium ions is on the a high concentration of sodium ions is on the outside of a membrane, and a high outside of a membrane, and a high concentration of potassium ions is on the concentration of potassium ions is on the inside of the cell.inside of the cell.b. b. Many negatively charged ions are inside a Many negatively charged ions are inside a cell.cell.c. c. In a resting cell, more positive ions leave In a resting cell, more positive ions leave than enter, so the outside of the cell membrane than enter, so the outside of the cell membrane develops a positive charge, while the inside develops a positive charge, while the inside develops a negative charge.develops a negative charge.


Potential ChangesPotential Changes

a. a. Stimulation of a membrane affects the Stimulation of a membrane affects the membrane’s resting potential.membrane’s resting potential.

b.b. When its resting potential becomes more When its resting potential becomes more positive, a membrane becomes depolarized.positive, a membrane becomes depolarized.

c.c. Potential changes are subject to summation. Potential changes are subject to summation.

d.d. Achieving threshold potential triggers an Achieving threshold potential triggers an action potential.action potential.


Action PotentialAction Potentiala. a. At threshold, sodium channels open, and sodium At threshold, sodium channels open, and sodium ions diffuse inward, depolarizing the membrane.ions diffuse inward, depolarizing the membrane.

b. b. About the same time, potassium channels open, and About the same time, potassium channels open, and potassium ions diffuse outward, repolarizing the potassium ions diffuse outward, repolarizing the membranemembrane

c. c. This rapid change in potential is an action potential.This rapid change in potential is an action potential.

d.d. Many action potentials can occur before active Many action potentials can occur before active transport re-establishes the resting potential.transport re-establishes the resting potential.

Nerve Impulses: Nerve Impulses: A wave of A wave of action potentials is a nerve action potentials is a nerve

impulse.impulse. Impulse ConductionImpulse Conduction

1.1. Unmyelinated fibers conduct impulses over the Unmyelinated fibers conduct impulses over the entire surface of the nerve.entire surface of the nerve.

2. Myelinated fibers conduct impulses more rapidly 2. Myelinated fibers conduct impulses more rapidly because the impulse jumps between the nodes of because the impulse jumps between the nodes of Ranvier.Ranvier.

3. Nerves with large diameters conduct impulses 3. Nerves with large diameters conduct impulses faster than those with small diameters.faster than those with small diameters.

Nerve ImpulsesNerve Impulses

All-or-None ResponseAll-or-None Response

1.1. A nerve impulse is conducted in an all-A nerve impulse is conducted in an all-or-none manner when a stimulus of or-none manner when a stimulus of threshold intensity is applied to a fiber.threshold intensity is applied to a fiber.

2. 2. All the impulses conducted on a fiber are All the impulses conducted on a fiber are of the same strength.of the same strength.

The Synapse – The Synapse – A synapse is the A synapse is the junction between two neurons.junction between two neurons.

Synaptic TransmissionSynaptic Transmission1. Impulses usually travel from a dendrite to a cell 1. Impulses usually travel from a dendrite to a cell

body, then along the axon to a synapse.body, then along the axon to a synapse.

2. Axons have synaptic knobs at their ends, which 2. Axons have synaptic knobs at their ends, which secrete neurotransmitters.secrete neurotransmitters.

3. A neurotransmitter is released when a nerve 3. A neurotransmitter is released when a nerve impulse reaches the end of an axon.impulse reaches the end of an axon.

4. A neurotransmitter reaching the nerve fiber on 4. A neurotransmitter reaching the nerve fiber on the distal side of the synaptic cleft triggers a the distal side of the synaptic cleft triggers a nerve impulse.nerve impulse.

The SynapseThe Synapse

The Synapse The Synapse

Excitatory and Inhibitory ActionsExcitatory and Inhibitory Actions1.1. Neurotransmitters that trigger nerve Neurotransmitters that trigger nerve

impulses are excitatory. Those that impulses are excitatory. Those that inhibit impulses are inhibitory.inhibit impulses are inhibitory.

2. 2. The net effect of synaptic knobs The net effect of synaptic knobs communicating with a neuron depends communicating with a neuron depends on which knobs are activated from on which knobs are activated from moment to moment.moment to moment.

The Synapse The Synapse NeurotransmittersNeurotransmitters

1.1. The nervous system produces many different The nervous system produces many different neurotransmitters, such as acetylcholine, neurotransmitters, such as acetylcholine, monoamines, amino acids, and peptides.monoamines, amino acids, and peptides.

2. A synaptic knob releases neurotransmitters 2. A synaptic knob releases neurotransmitters when an action potential increases membrane when an action potential increases membrane permeability to calcium ions.permeability to calcium ions.

3. After being released, neurotransmitters are 3. After being released, neurotransmitters are decomposed or removed from synaptic clefts.decomposed or removed from synaptic clefts.

Types of Nerves Types of Nerves

Nerves are cordlike bundles of nerve fibers Nerves are cordlike bundles of nerve fibers held together by layers of connective held together by layers of connective tissue.tissue.

Types of NervesTypes of Nerves

1. Sensory Nerves – 1. Sensory Nerves – conduct impulses conduct impulses into the brain or spinal cordinto the brain or spinal cord

2. Motor Nerves –2. Motor Nerves – carry impulses to carry impulses to muscles or glandsmuscles or glands

3. Mixed nerves –3. Mixed nerves – include both sensory include both sensory and motor fibersand motor fibers

Nerve Pathways Nerve Pathways

A nerve pathway is a route an impulse A nerve pathway is a route an impulse follows through the nervous sytem.follows through the nervous sytem.

Nerve PathwaysNerve Pathways

Reflex arc – Reflex arc – usually includes a sensory usually includes a sensory neuron, a reflex center composed of an neuron, a reflex center composed of an interneuron, and a motor neuroninterneuron, and a motor neuron

Reflex BehaviorReflex Behavior1. 1. Reflexes are autonomic, subconscious Reflexes are autonomic, subconscious

responses to changes (stimuli) within or responses to changes (stimuli) within or outside the body.outside the body.

2. Reflexes help maintain homeostasis by 2. Reflexes help maintain homeostasis by controlling may involuntary processes.controlling may involuntary processes.

3. Reflexes carry out autonomic actions of 3. Reflexes carry out autonomic actions of swallowing, sneezing, coughing, and swallowing, sneezing, coughing, and vomiting.vomiting.

4. The knee-jerk reflex (patellar tendon 4. The knee-jerk reflex (patellar tendon reflex) employs two neurons (sensory reflex) employs two neurons (sensory and motor). and motor).

5. Withdrawal reflexes are protective. 5. Withdrawal reflexes are protective. Employs all three types of nerves.Employs all three types of nerves.

Meninges Meninges

Meninges are membranes that lie between Meninges are membranes that lie between the bones and soft tissues of the cranial the bones and soft tissues of the cranial cavity and vertebral canal. They protect cavity and vertebral canal. They protect the brain and spinal cord the brain and spinal cord

MeningesMeningesThey consists of three layers:They consists of three layers:

1. Dura Mater – 1. Dura Mater – outermost layeroutermost layer

2. Arachnoid Mater –2. Arachnoid Mater – located between the dura and pia located between the dura and pia matermater

a. Subarachnoid space – a. Subarachnoid space – lies between the arachnoid and pia lies between the arachnoid and pia mater and contains the clear watery mater and contains the clear watery cerebrospinal fluid cerebrospinal fluid (CFS)(CFS)

3. Pia Mater – 3. Pia Mater – very thin and contains nerves and blood very thin and contains nerves and blood vessels that nourish underlying cells of the brain and vessels that nourish underlying cells of the brain and spinal cord; hugs the surface of these organs spinal cord; hugs the surface of these organs following their irregular contours, passing over high following their irregular contours, passing over high areas and dipping into depressionsareas and dipping into depressions

Spinal Cord Spinal Cord

The spinal cord is a The spinal cord is a nerve column that nerve column that extends from the extends from the brain into the brain into the vertebral canal.vertebral canal.

Structure of the Spinal Structure of the Spinal CordCord

The spinal cord is composed of thirty-one The spinal cord is composed of thirty-one segments, each of which gives rise to a segments, each of which gives rise to a pair of spinal nerves.pair of spinal nerves.

The spinal cord has a The spinal cord has a cervical cervical enlargementenlargement, which gives off nerves to , which gives off nerves to the upper limbs, and a the upper limbs, and a lumbar lumbar enlargementenlargement, which gives off nerves to , which gives off nerves to the lower limbsthe lower limbs..

Spinal NervesSpinal Nerves

Structure of the Spinal Structure of the Spinal CordCord Two grooves, a deep Two grooves, a deep

anterior fissureanterior fissure and a and a shallow shallow posterior median posterior median sulcussulcus, extend the length , extend the length of the spinal cord, dividing of the spinal cord, dividing it into right and left halves.it into right and left halves.

It has a central core of gray It has a central core of gray matter within white matter.matter within white matter.

The white matter is The white matter is composed of bundles of composed of bundles of myelinated nerve fibers myelinated nerve fibers that comprise major nerve that comprise major nerve pathways called nerve pathways called nerve tracts.tracts.

Functions of the Spinal Functions of the Spinal CordCord

Conduction of Nerve Impulses – Conduction of Nerve Impulses – provides a two-way communication provides a two-way communication system between the brain and body system between the brain and body parts. parts. Ascending tractsAscending tracts carry sensory carry sensory information to the brain and information to the brain and descending tractsdescending tracts conduct motor conduct motor impulses from the brain to muscles impulses from the brain to muscles and glands.and glands.

Center for Spinal ReflexesCenter for Spinal Reflexes

The BrainThe Brain

Structures of the Structures of the CerebrumCerebrum

Cerebral Hemisphere – Cerebral Hemisphere – 2 large masses 2 large masses which are essentially mirror images of which are essentially mirror images of each other connected by a deep bridge each other connected by a deep bridge of nerve fibers called the of nerve fibers called the corpus corpus callosumcallosum; the surface has many ; the surface has many convolutionsconvolutions (ridges) separated by (ridges) separated by grooves (shallow groove is called a grooves (shallow groove is called a sulcussulcus and a deep groove is called a and a deep groove is called a fissurefissure) )

The lobes of the cerebral hemisphere The lobes of the cerebral hemisphere are named after the skull bones are named after the skull bones they underlie:they underlie: Frontal LobeFrontal Lobe Parietal LobeParietal Lobe Temporal LobeTemporal Lobe Occipital LobeOccipital Lobe

Structures of the Structures of the CerebrumCerebrum

Cerebral Cortex Cerebral Cortex

thin layer of gray matter thin layer of gray matter that forms the that forms the outermost portion of outermost portion of the cerebrum; the cerebrum; contains nearly 75% contains nearly 75% of all the neuron cell of all the neuron cell bodies in the bodies in the nervous systemnervous system

Mass of White Matter Mass of White Matter

lies just beneath the lies just beneath the cerebral cortex and cerebral cortex and makes up the bulk makes up the bulk of the cerebrum; of the cerebrum; bundles of bundles of myelinated fibersmyelinated fibers

Functions of the Functions of the Cerebrum Cerebrum

Functional Regions of the Functional Regions of the Cerebral Cortex Cerebral Cortex

Primary Motor Areas – Primary Motor Areas – lie in the frontal lie in the frontal lobes; fibers cross over in the brain stem lobes; fibers cross over in the brain stem from one side of the brain to the other from one side of the brain to the other (right CH motor area generally controls (right CH motor area generally controls skeletal muscles on the left side of the skeletal muscles on the left side of the body and vise versa)body and vise versa)

motor speech motor speech areaarea

frontal eye frontal eye fieldfield

Functional Regions of the Functional Regions of the Cerebral CortexCerebral Cortex

Sensory Areas – Sensory Areas – located located in several lobesin several lobes

a. cutaneous senses – a. cutaneous senses – sensations of the skinsensations of the skin

b.b. visual areavisual area

c. auditory areac. auditory area

d. taste aread. taste area

e. smell areae. smell area


Association Area – Association Area – neither primarily neither primarily sensory or motor; sensory or motor; analyzes and analyzes and interpretsinterprets sensory sensory experiences and experiences and oversees memory, oversees memory, reasoning, verbalizing, reasoning, verbalizing, judgment, and judgment, and emotionemotion


General Interpretive General Interpretive Area – Area – complex complex thought processingthought processing

Hemisphere Dominance Hemisphere Dominance

Although both cerebral hemispheres Although both cerebral hemispheres participate in basic functions, in most participate in basic functions, in most people, one side of the cerebrum is the people, one side of the cerebrum is the dominant hemispheredominant hemisphere, controlling other , controlling other functions.functions.

Hemisphere DominanceHemisphere Dominance

In over 90% of the population, the left In over 90% of the population, the left hemisphere is dominant for language-hemisphere is dominant for language-related activities of speech, writing, reading, related activities of speech, writing, reading, and for complex intellectual functions and for complex intellectual functions requiring verbal, analytical, and requiring verbal, analytical, and computational skills.computational skills.

Hemisphere DominanceHemisphere Dominance

In addition to carrying on basic In addition to carrying on basic functions, the non-dominant functions, the non-dominant hemisphere specializes in nonverbal hemisphere specializes in nonverbal functions, such as motor tasks that functions, such as motor tasks that require orientation of body in space, require orientation of body in space, understanding, and interpreting understanding, and interpreting musical patterns, and nonverbal visual musical patterns, and nonverbal visual experiences, as well as emotional and experiences, as well as emotional and intuitive thinking.intuitive thinking.

Cerebrospinal Fluid Cerebrospinal Fluid

Cerebrospinal Fluid is secreted by Cerebrospinal Fluid is secreted by capillaries from the pia mater.capillaries from the pia mater.

It completely surrounds the brain and It completely surrounds the brain and spinal cord.spinal cord.

These organs float in the fluid, which These organs float in the fluid, which supports and protects them.supports and protects them.

It also provides a pathway to the blood for It also provides a pathway to the blood for wastewaste

Diencephalon Diencephalon

The diencephalon The diencephalon is located between the is located between the cerebral hemispheres and above the cerebral hemispheres and above the midbrain. midbrain.

It is largely composed of gray matterIt is largely composed of gray matter

DiencephalonDiencephalon

Thalamus – Thalamus – relay relay station for sensory station for sensory impulses (except impulses (except smell); produces a smell); produces a general awareness general awareness of certain of certain sensations, such as sensations, such as pain, touch, and pain, touch, and temperaturetemperature

DiencephalonDiencephalonHypothalamus – Hypothalamus – below thalamus; maintains below thalamus; maintains

homeostasis by regulating a variety of visceral homeostasis by regulating a variety of visceral activities and by linking the nervous and endocrine activities and by linking the nervous and endocrine systems; regulates:systems; regulates: heart rate and arterial blood pressureheart rate and arterial blood pressure body temperaturebody temperature water and electrolyte balancewater and electrolyte balance control of hunger and body weightcontrol of hunger and body weight control of movements and glandular secretions of stomach control of movements and glandular secretions of stomach

and intestinesand intestines production of neurosecretory substances that stimulate the production of neurosecretory substances that stimulate the

pituitary gland to secrete hormonespituitary gland to secrete hormones sleep and wakefulnesssleep and wakefulness

HypothalamusHypothalamus

DiencephalonDiencephalon

Limbic System – Limbic System – controls emotional controls emotional experiences and expression; can experiences and expression; can modify the way a person acts by modify the way a person acts by producing such feelings as fear, anger, producing such feelings as fear, anger, pleasure, and sorrow; recognizes pleasure, and sorrow; recognizes upsets in a person’s physical and upsets in a person’s physical and psychological condition that might psychological condition that might threaten life; guides a person into threaten life; guides a person into behavior that is likely to increase the behavior that is likely to increase the chance of survivalchance of survival

Limbic SystemLimbic System

Other Structures of the Other Structures of the DiencephalonDiencephalon

1. Optic Tract Optic Chiasma1. Optic Tract Optic Chiasma

2. infundibulum – 2. infundibulum – structures in which the structures in which the pituitary gland is attachedpituitary gland is attached

3. pituitary gland3. pituitary gland

4. olfactory bulbs4. olfactory bulbs

5. pineal gland5. pineal gland – structure that secretes – structure that secretes melatonin, which affects the sleep cycle; melatonin, which affects the sleep cycle; the darker it is the more melatonin is the darker it is the more melatonin is released, the lighter it is the less melatonin released, the lighter it is the less melatonin is releasedis released

optic tracts and optic optic tracts and optic chiasmachiasma

infundibulum – infundibulum – structures in which structures in which the pituitary gland is attachedthe pituitary gland is attached

pituitary glandpituitary gland

olfactory bulbsolfactory bulbs

pineal gland pineal gland

structure that secretes structure that secretes melatonin, which melatonin, which affects the sleep affects the sleep cycle; the darker it is cycle; the darker it is the more melatonin is the more melatonin is released, the lighter released, the lighter it is the less it is the less melatonin is released melatonin is released

Brain Stem Brain Stem

a bundle of nerve a bundle of nerve tissue that tissue that connects the connects the cerebrum to the cerebrum to the spinal cordspinal cord

Midbrain Midbrain

joins lower parts of the joins lower parts of the brain stem and brain stem and spinal cord with spinal cord with higher parts of the higher parts of the brain; contains brain; contains centers for certain centers for certain visual and auditory visual and auditory reflexesreflexes

Pons Pons rounded bulges on the rounded bulges on the

underside of the brain underside of the brain stem; transmits impulses stem; transmits impulses to and from the cerebrum to and from the cerebrum and medulla oblongata and medulla oblongata and the cerebrum and and the cerebrum and cerebellum; relays cerebellum; relays messages from the PNS messages from the PNS to high brain centers and to high brain centers and functions with the medulla functions with the medulla oblongata in regulating oblongata in regulating the rate and depth of the rate and depth of breathing breathing

Medulla Oblongata Medulla Oblongata All descending and ascending nerve fibers pass All descending and ascending nerve fibers pass

through the medulla oblongata.through the medulla oblongata.It is composed of gray matter surrounded by It is composed of gray matter surrounded by

white matter and contains contains centers for white matter and contains contains centers for controlling visceral activities:controlling visceral activities:

a.a. cardiac center – cardiac center – alters heart ratealters heart rate

b. vasomotor center – b. vasomotor center – certain cells initiate impulses certain cells initiate impulses which stimulate blood vessels towhich stimulate blood vessels to contract contract ((vasoconstrictionvasoconstriction) elevating blood pressure; other ) elevating blood pressure; other cells have the opposite affect – dilating blood vessels cells have the opposite affect – dilating blood vessels ((vasodilationvasodilation) dropping blood pressure) dropping blood pressure

c. respiratory center – c. respiratory center – acts with centers in the pons to acts with centers in the pons to regulate the rate, rhythm, and depth of breathingregulate the rate, rhythm, and depth of breathing

Medulla OblongataMedulla Oblongata

Reticular Formation Reticular Formation (reticular activating system) (reticular activating system)

The reticular formation extends from the upper The reticular formation extends from the upper portion of the spinal cord into the portion of the spinal cord into the diencephalon and is connected to all diencephalon and is connected to all ascending and descending fiber tracts.ascending and descending fiber tracts.

When sensory impulses are received it activates When sensory impulses are received it activates the cerebral cortex into wakefulness.the cerebral cortex into wakefulness.

Without this arousal, the cortex remains unaware Without this arousal, the cortex remains unaware of stimulation and cannot interpret of stimulation and cannot interpret information or carry out thought processes.information or carry out thought processes.

Decreased activity results in sleep.Decreased activity results in sleep.Injury to it causes a person to be unconscious Injury to it causes a person to be unconscious

and cannot be aroused, even with strong and cannot be aroused, even with strong stimulation (comatose state).stimulation (comatose state).

Cerebellum Cerebellum

large mass located large mass located below the occipital below the occipital lobes and posterior lobes and posterior to the pons and to the pons and medulla oblongata;medulla oblongata;

two hemispheres two hemispheres composed largely of composed largely of white matter white matter surrounded by a thin surrounded by a thin layer of gray matter; layer of gray matter;

CerebellumCerebellumcommunicates with other parts of the CNS by means communicates with other parts of the CNS by means

of three pairs of nerve tracts called of three pairs of nerve tracts called cerebellar cerebellar pedunclespeduncles::

a. inferior peduncle – a. inferior peduncle – brings sensory information brings sensory information concerning the position of the limbs, joints, and other concerning the position of the limbs, joints, and other body parts to the cerebellumbody parts to the cerebellum

b. middle peduncle – b. middle peduncle – transmits signals from the transmits signals from the cerebral cortex to the cerebellum concerning the cerebral cortex to the cerebellum concerning the desired positions of the above mentioned parts; after desired positions of the above mentioned parts; after integrating and analyzing this information the integrating and analyzing this information the cerebellum sends correcting information via the cerebellum sends correcting information via the superior pedunclesuperior peduncle

CerebellumCerebellum

CerebellumCerebellumThus, the cerebellum is a reflex center Thus, the cerebellum is a reflex center

for integrating sensory information for integrating sensory information concerning position of the body parts concerning position of the body parts and for coordinating complex skeletal and for coordinating complex skeletal muscle movements. muscle movements.

Damage is likely to result in tremors, Damage is likely to result in tremors, inaccurate movements of voluntary inaccurate movements of voluntary muscles, loss of muscle tone, a muscles, loss of muscle tone, a reeling walk, and loss of equilibrium.reeling walk, and loss of equilibrium.

Peripheral Nervous Peripheral Nervous SystemSystem

Somatic Nervous System Somatic Nervous System

The somatic nervous system consists of The somatic nervous system consists of the cranial and spinal nerve fibers that the cranial and spinal nerve fibers that connect the CNS to the skin and connect the CNS to the skin and skeletal muscles.skeletal muscles.

It oversees conscious activities.It oversees conscious activities.

Autonomic Nervous Autonomic Nervous SystemSystemThe autonomic nervous system consists of sensory The autonomic nervous system consists of sensory

neurons and motor neurons that run between the neurons and motor neurons that run between the central nervous system (especially the central nervous system (especially the hypothalamushypothalamus and and medulla oblongatamedulla oblongata) and ) and various internal organs such as the: various internal organs such as the:

heart heart lungs lungs viscera viscera glands (both exocrine and endocrine) glands (both exocrine and endocrine)

Autonomic Nervous Autonomic Nervous System System

The autonomic nervous system is the portion of the PNS The autonomic nervous system is the portion of the PNS that functions independently (autonomously) and that functions independently (autonomously) and continuously without conscious effort.continuously without conscious effort.

1.1. It controls visceral functions by regulating the actions It controls visceral functions by regulating the actions of smooth muscles, cardiac muscles, and glands.of smooth muscles, cardiac muscles, and glands.

2. It regulates heart rate, blood pressure, breathing rate, 2. It regulates heart rate, blood pressure, breathing rate, body temperature, and other visceral activities that body temperature, and other visceral activities that maintain homeostasis.maintain homeostasis.

3. Portions respond to emotional stress and prepare the 3. Portions respond to emotional stress and prepare the body to meet demands of strenuous physical activity body to meet demands of strenuous physical activity

Autonomic Nervous Autonomic Nervous SystemSystem

General Characteristics:General Characteristics:1.1. regulated by reflexesregulated by reflexes2.2. typically, peripheral nerve fibers lead to typically, peripheral nerve fibers lead to

ganglia outside the CNS where they are ganglia outside the CNS where they are integrated and relayed back to viscera integrated and relayed back to viscera (muscles and glands) that respond by (muscles and glands) that respond by contracting, releasing secretions, or being contracting, releasing secretions, or being inhibitedinhibited

3.3. provides the autonomic system with a provides the autonomic system with a degree of independence from the brain and degree of independence from the brain and spinal cord includes two divisions:spinal cord includes two divisions:


The autonomic nervous system includes two The autonomic nervous system includes two divisions:divisions:

Sympathetic division – Sympathetic division – prepares the body for prepares the body for energy-expending, stressful, or emergency energy-expending, stressful, or emergency situationssituations

Parasympathetic division –Parasympathetic division – most active during most active during ordinary, restful conditions; counterbalances ordinary, restful conditions; counterbalances the effects of the sympathetic division and the effects of the sympathetic division and restores the body to a resting state following restores the body to a resting state following a stressful experiencea stressful experience

Sympathetic divisionSympathetic division

The The preganglionicpreganglionic motor motor neurons of the neurons of the sympathetic system sympathetic system (shown in black) arise in (shown in black) arise in the spinal cord. They the spinal cord. They pass into sympathetic pass into sympathetic ganglia which are ganglia which are organized into two organized into two chains that run parallel to chains that run parallel to and on either side of the and on either side of the spinal cord. spinal cord.

Sympathetic divisionSympathetic divisionThe preganglionic neuron may do one of three things in the The preganglionic neuron may do one of three things in the

sympathetic ganglion: sympathetic ganglion: synapse with synapse with postganglionicpostganglionic neurons (shown in white) which neurons (shown in white) which

then reenter the spinal nerve and ultimately pass out to the sweat then reenter the spinal nerve and ultimately pass out to the sweat glands and the walls of blood vessels near the surface of the glands and the walls of blood vessels near the surface of the body. body.

pass up or down the sympathetic chain and finally synapse with pass up or down the sympathetic chain and finally synapse with postganglionic neurons in a higher or lower ganglionpostganglionic neurons in a higher or lower ganglion

leave the ganglion by way of a cord leading to special ganglia leave the ganglion by way of a cord leading to special ganglia (e.g. the solar plexus) in the viscera. Here it may synapse with (e.g. the solar plexus) in the viscera. Here it may synapse with postganglionic sympathetic neurons running to the smooth postganglionic sympathetic neurons running to the smooth muscular walls of the viscera. However, some of these muscular walls of the viscera. However, some of these preganglionic neurons pass right on through this second ganglion preganglionic neurons pass right on through this second ganglion and into the and into the adrenal medullaadrenal medulla. Here they synapse with the highly-. Here they synapse with the highly-modified postganglionic cells that make up the secretory portion modified postganglionic cells that make up the secretory portion of the adrenal medulla. of the adrenal medulla.


The neurotransmitter of the preganglionic The neurotransmitter of the preganglionic sympathetic neurons is sympathetic neurons is acetylcholineacetylcholine ( (AChACh). It ). It stimulates action potentials in the postganglionic stimulates action potentials in the postganglionic neurons. neurons.

The neurotransmitter released by the The neurotransmitter released by the postganglionic neurons is postganglionic neurons is noradrenalinenoradrenaline (also (also called called norepinephrinenorepinephrine). ).

The action of noradrenaline on a particular gland or The action of noradrenaline on a particular gland or muscle is excitatory is some cases, inhibitory in muscle is excitatory is some cases, inhibitory in others. (At excitatory terminals, ATP may be others. (At excitatory terminals, ATP may be released along with noradrenaline.) released along with noradrenaline.)

Sympathetic divisionSympathetic divisionThe The release of noradrenalinerelease of noradrenaline

stimulates heartbeat stimulates heartbeat raises blood pressure raises blood pressure dilates the pupils dilates the pupils dilates the trachea and bronchi dilates the trachea and bronchi stimulates glycogenolysis — the conversion of liver glycogen into stimulates glycogenolysis — the conversion of liver glycogen into

glucose glucose shunts blood away from the skin and viscera to the skeletal muscles, shunts blood away from the skin and viscera to the skeletal muscles,

brain, and heart brain, and heart inhibits peristalsis in the gastrointestinal (GI) tract inhibits peristalsis in the gastrointestinal (GI) tract inhibits contraction of the bladder and rectum inhibits contraction of the bladder and rectum and, at least in rats and mice, increases the number of AMPA and, at least in rats and mice, increases the number of AMPA

receptors in the hippocampus and thus increases long-term receptors in the hippocampus and thus increases long-term potentiation (LTP). potentiation (LTP).


In short, stimulation of the sympathetic branch of In short, stimulation of the sympathetic branch of the autonomic nervous system prepares the body the autonomic nervous system prepares the body for emergencies: for "for emergencies: for "fight or flightfight or flight" (and, " (and, perhaps, enhances the memory of the event that perhaps, enhances the memory of the event that triggered the response). triggered the response).

Activation of the sympathetic system is quite Activation of the sympathetic system is quite general because a single preganglionic neuron general because a single preganglionic neuron usually synapses with many postganglionic usually synapses with many postganglionic neurons; the release of neurons; the release of adrenalineadrenaline from the from the adrenal medulla into the blood ensures that all the adrenal medulla into the blood ensures that all the cells of the body will be exposed to sympathetic cells of the body will be exposed to sympathetic stimulation even if no postganglionic neurons stimulation even if no postganglionic neurons reach them directly. reach them directly.

Parasympathetic Nervous Parasympathetic Nervous System System

The main nerves of the parasympathetic The main nerves of the parasympathetic system are the tenth cranial nerves, the system are the tenth cranial nerves, the vagus nervesvagus nerves. They originate in the . They originate in the medulla oblongatamedulla oblongata. Other preganglionic . Other preganglionic parasympathetic neurons also extend parasympathetic neurons also extend from the brain as well as from the lower from the brain as well as from the lower tip of the spinal cord. tip of the spinal cord.

Parasympathetic Nervous Parasympathetic Nervous SystemSystem

Each preganglionic parasympathetic neuron Each preganglionic parasympathetic neuron synapses with just a few postganglionic synapses with just a few postganglionic neurons, which are located near — or in — the neurons, which are located near — or in — the effector organ, a muscle or gland. effector organ, a muscle or gland.

AcetylcholineAcetylcholine ( (AChACh) is the neurotransmitter at ) is the neurotransmitter at all the pre- and many of the postganglionic all the pre- and many of the postganglionic neurons of the parasympathetic system. neurons of the parasympathetic system. However, some of the postganglionic neurons However, some of the postganglionic neurons release nitric oxide (NO) as their release nitric oxide (NO) as their neurotransmitter. neurotransmitter.


Parasympathetic stimulationParasympathetic stimulation causes: causes: slowing down of the heartbeat lowering of slowing down of the heartbeat lowering of

blood pressure blood pressure constriction of the pupils constriction of the pupils increased blood flow to the skin and increased blood flow to the skin and

viscera viscera peristalsis of the GI tract peristalsis of the GI tract


In short, the parasympathetic system In short, the parasympathetic system returns the body functions to normal after returns the body functions to normal after they have been altered by sympathetic they have been altered by sympathetic stimulation. In times of danger, the stimulation. In times of danger, the sympathetic system prepares the body sympathetic system prepares the body for violent activity. The parasympathetic for violent activity. The parasympathetic system reverses these changes when the system reverses these changes when the danger is over. danger is over.


The vagus nerves also help keep inflammation The vagus nerves also help keep inflammation under control. Inflammation stimulates nearby under control. Inflammation stimulates nearby sensory neurons of the vagus. When these sensory neurons of the vagus. When these nerve impulses reach the medulla oblongata, nerve impulses reach the medulla oblongata, they are relayed back along motor fibers to the they are relayed back along motor fibers to the inflamed area. The acetylcholine from the inflamed area. The acetylcholine from the motor neurons suppresses the release of motor neurons suppresses the release of inflammatory cytokines, e.g., tumor necrosis inflammatory cytokines, e.g., tumor necrosis factor (TNF), from macrophages in the factor (TNF), from macrophages in the inflamed tissue. inflamed tissue.


Although the autonomic nervous system is Although the autonomic nervous system is considered to be involuntary, this is not entirely considered to be involuntary, this is not entirely true. A certain amount of conscious control can true. A certain amount of conscious control can be exerted over it as has long been be exerted over it as has long been demonstrated by practitioners of Yoga and Zen demonstrated by practitioners of Yoga and Zen Buddhism. During their periods of meditation, Buddhism. During their periods of meditation, these people are clearly able to alter a number these people are clearly able to alter a number of autonomic functions including heart rate and of autonomic functions including heart rate and the rate of oxygen consumption. These the rate of oxygen consumption. These changes are not simply a reflection of changes are not simply a reflection of decreased physical activity because they decreased physical activity because they exceed the amount of change occurring during exceed the amount of change occurring during sleep or hypnosis. sleep or hypnosis.


Cranial Nerves Cranial Nerves 1.1. 12 pairs12 pairs

2.2. arise from the underside of the brain; except arise from the underside of the brain; except for the first pair, which begins within the for the first pair, which begins within the cerebrumcerebrum

3.3. lead to parts of the head, neck, and trunklead to parts of the head, neck, and trunk

4.4. most are mixed nerves, but some associated most are mixed nerves, but some associated with smell and vision contain only sensory with smell and vision contain only sensory fibersfibers

5.5. some that control muscles and glands in this some that control muscles and glands in this area are primarily motor fibersarea are primarily motor fibers

Cranial NervesCranial Nerves

Nerves Type Function

I Olfactorysensory olfaction (smell)

II Optic sensoryvision

(Contain 38% of all the axons connecting to the brain.)

III Oculomotor motor* eyelid and eyeball muscles

IV Trochlear motor* eyeball muscles

V Trigamental mixedSensory: facial and mouth sensation

Motor: chewing

VI Abducens motor* eyeball movement

VII Facial mixedSensory: taste

Motor: facial muscles and salivary glands

VIII Vestibulocochlear

sensory hearing and balance

IX Glossopharyngealmixed

Sensory: tasteMotor: swallowing

X Vagus mixedmain nerve of the

parasympathetic nervous system (PNS)

XI Accesory motor swallowing; moving head and shoulder

XII Hypoglossal motor* tongue muscles

Spinal Nerves Spinal Nerves

1.1. 31 pairs31 pairs

2.2. originate from the spinal cordoriginate from the spinal cord

3.3. All of the spinal nerves are "mixed"; that All of the spinal nerves are "mixed"; that is, they contain both sensory and motor is, they contain both sensory and motor neurons. They provide two way neurons. They provide two way communication between the spinal cord communication between the spinal cord and parts of the upper and lower limbs, and parts of the upper and lower limbs, neck, and trunk. neck, and trunk.


Spinal nerves are grouped according to the Spinal nerves are grouped according to the level in which they arise:level in which they arise:

cervical nerves (C1-C8) – cervical nerves (C1-C8) – 8 pairs8 pairs thoracic nerves (T1-T12) – thoracic nerves (T1-T12) – 12 pairs12 pairs lumbar nerves (L1-L5) – lumbar nerves (L1-L5) – 5 pairs5 pairs sacral nerves (S1-S5) – sacral nerves (S1-S5) – 5 pairs5 pairs coccygeal nerve (C0) –coccygeal nerve (C0) – one pair one pair


The adult spinal cord ends at the level The adult spinal cord ends at the level between the first and second lumbar between the first and second lumbar vertebrae, so the lumbar, sacral, and vertebrae, so the lumbar, sacral, and coccygeal nerves descend beyond the coccygeal nerves descend beyond the end of the cord, forming a structure end of the cord, forming a structure called the called the cauda equina cauda equina (horse’s tail).(horse’s tail).


Documents

The Nervous System. Introduction Organs of the nervous system are divided into the Central (CNS) and the Peripheral (PNS) nervous systems. These structures