Nervous System

•One of 2 controlling and communicating systems of the body (other is the endocrine system)•-Sensory input - Integration - Motor output

-The two principal cell types of the nervous system are:–Neurons

•hundreds of thousands of neurons extend axons and make synapses all over the body with other neurons, muscles and glands•communicate through action potentials •allows for short response times to changes in homeostasis (excitable cells)

–Neuroglia •guide developing neurons to make synapses•provide a supportive scaffolding for developed neurons ( a supportive cell)

Organization of the Nervous System

•Central nervous system (CNS) -BRAIN and SPINAL C.–consists of the brain located within the skull and the spinal cord located within the vertebral foramen

•large masses of neurons

–integration and command center of the body –covered by meninges and surrounded by cerebrospinal fluid

•Peripheral nervous system (PNS)–consists of neurons that bridge the gap between the CNS that extend to other locations in the body

•propagate APs to and away from the CNS

–the neurons are organized into nerves (bundle of axons) and ganglions (group of cell bodies outside the CNS)

- carries messages to and from the spinal cord

Anatomical Organization of the Nervous System

Nerves•Nerve

–cordlike organ of the PNS consisting of axons enclosed by connective tissue

Connective tissue coverings include:–Endoneurium

•loose connective tissue that surrounds each individual axon

–Perineurium•coarse connective tissue that bundles axons into fascicles

–Epineurium•tough fibrous connective tissue around a nerve

Structure of a Nerve

Functional Organization of the Nervous System

Functions of the Nervous System-Transmit sensory information

–propagate APs to the CNS following a stimulus which has changed a variable from its set point

•from eyes, skin, blood vessels, ears, digestive tract, joints, muscles, lungs…

•Integration–interpretation of sensory information by the CNS

•type, location and magnitude of stimulus

•Transmit motor information–propagate APs from the CNS to various effector organs throughout the body

•provides a way to respond to stimuli

Neuron Types of the Nervous System

•Sensory (afferent)–associated with sensory receptors–propagate APs via the PNS toward the CNS

•Interneurons–integrate information within the CNS–receive APs from sensory neurons and initiate APs in motor neurons (shuttle signals thru CNS)

•Motor (efferent)–propagate APs via the PNS away from the CNS to effectors

Basic Function of the Nervous System

Sensory Receptors•Structures specialized to respond to stimuli:

–nerve endings (dendrites of neurons)–sense organs

•nerve endings combined with other tissue types to enhance detection of a stimuli

–example: taste buds•Mechanoreceptors

–respond to touch, pressure, stretch and itch

•Thermoreceptors –respond to changes in temperature

•Photoreceptors –respond to light

•Chemoreceptors –respond to chemicals

•Nociceptors –respond to pain

Neural Integration of the CNS• Qualitative information (salty, pain or temperature) depends

upon which neurons are propagating APs• Quantitative (strength) information depend on:

– the number of neurons that are firing APs – the frequency of APs fired per neuron

Myelination of Neurons of the Nervous System

-Some neurons in the CNS are myelinated, while most are unmyelinated

-All of the neurons in the PNS are myelinated

•Areas of the CNS that are made of myelinated neurons are called white matter

–represent the locations of long sensory and motor neurons

•Areas of the CNS that are made of unmyelinated neurons are called gray matter

-represent the locations of short interneurons which make many synapses for integration to process sensory information and initiate motor information

Reflexes

-A rapid, predictable motor response to a stimulus

•Reflexes can be: –simple

•involve peripheral nerves and the spinal cord–spinal reflexes (Inborn = intrinsic = innate)

–learned (acquired)•involve peripheral nerves and the brain

•Following a stimulus, the sensory and motor information of a reflex follows a pathway called a reflex arc

–in many spinal reflexes, the effector is nearby the location of the stimulus

-May involve only peripheral nerves and spinal nerves

-May involve Higher brain centers as well

-That is, the brain may be informed later (after the reflex

has occurred)

Reflex Arc•There are five components of a reflex arc

–Receptor •respond to stimulus

–Sensory neuron •transmits the afferent impulse to the CNS

–Integration (control) center•region within the CNS where synapses (processing of sensory info) occur (brain or s.cord)

–Motor neuron •sends efferent information to an effector

–Effector •muscle fiber or gland that responds to the efferent impulse•the activity of the effector depends upon the magnitude of the stimulus

-Reflexes are to limit damage i.e. to protect quickly

Meninges and CSF

-The meninges are 3 connective tissue membranes that lie external to the brain and the spinal cord

–dura mater–arachnoid mater–pia mater

–cover and protect the CNS –hold cerebrospinal fluid (CSF) –prevents harmful substances from entering CSF

•The CSF is the extracellular fluid of the cells of the nervous system

–surrounds and fills the spaces within the spinal cord and the brain

–prevents the brain from crushing under its own weight

•protects the CNS from trauma

Meninges-- connective tissue surrounding spinal cord and brain (continuous with each other)

1. Dura Mater - most superficial

- dense irregular connective tissue

2. Arachnoid - middle layer

-avascular (no blood vessels)

- spider web arrangement of delicate collagen fibers and some elastic

3. Pia Mater - thin transparent connective tissue that adheres to surface of brain or spinal cord

- interlacing bundles of collagen and fine elastic fibers

- contains many blood vessels to supply oxygen and nutrients

Meninges

Brain

• 4 lobes– frontal, parietal, temporal and occipital– location of interneurons for perception of all senses– Site of memory, emotion, learning– site of initiation of voluntary skeletal muscle contraction

Cerebrum

- largest portion of the brain, about 2/3

-upper most portion and divided into 2 hemispheres

Cerebral cortex

-Outermost portion of cerebrum

-human cerebral cortex is more developed than in any other animal

• -superficial is called gray matter• 40% of brain mass• -enables sensaton, communcation. Memory, understanding• Hemispheres are contralateral i.e. left side of brain controls

left side of face but right side of body

• -no functional area acts alone i.e. behavior involves entire cortex

The Cerebellum-Located dorsal to the pons and medulla

-Protrudes under the occipital lobes of the cerebrum

-Makes up 11% of the brain’s mass

•Modifies the motor information leaving the motor cortex

–provides precise timing and appropriate patterns of skeletal muscle contraction to maintain balance and coordination

Cerebellar activity occurs subconsciously

Responsible for balance and coordination

Brain Stem-Comprised of the pons and the medulla oblongata

-Clusters of neurons (brain centers) in regions of the pons and medulla control the basic life functions:

–heart rate•controlled by the cardioacceleratory and cardioinhibitory centers in the medulla

–blood pressure•controlled by the cardioacceleratory, cardioinhibitory, and vasomotor centers in the medulla

–breathing rate•controlled by the inspiratory and expiratory centers in the medulla and pons, respectively

•Control of effectors occurs through the Autonomic Nervous System•Provides pathways between higher and lower brain centers

Brain

Hypothalamus and Pituitary

•Hypothalamus and Pituitary (Master glands) (caps Brain stem)

–2 glands located inferior to the thalamus–Secrete hormones which regulate a large number of metabolic processes

•metabolic rate•sex hormone levels in the blood•growth•water balance•blood nutrient levels

-The hypothalamus secretes hormones which in turn cause the pituitary to secrete hormones, thus the hypothalamus controls the function of the pituitary

Hypothalmus regulates blood pressure, heart rate, force of heart

rate, rate of breathing

Perception of pleasure, maintains body temperature

Feelings of hunger and regulates sleep

Spinal Cord

•The spinal cord is attached to the brain and extends to the lumbar region of the vertebral column

•Functions include:–integration of basic stimuli presented to the body below the neck through simple reflexes

•withdrawal reflex in response to pain

-sending sensory and motor information to and from the brain

31 pairs of spinal nerves.There are enlargements in the

cervical and lumbar regions where nerves of limbs emerge.

Cauda equina is a collection of nerve roots at the inferior end of

the vertebral column

Spinal Cord Anatomy

•Dorsal (posterior) horns (left and right)–sensory information enter the cord on the dorsal aspect where they synapse with interneurons or motor neurons

-extend into dorsal roots and ganglia

•Ventral (anterior) horns (left and right)–motor information exits the cord on the ventral aspect where they control effectors (muscle or glands)

-extend into motor roots

-Dorsal and ventral roots merge together to form spinal nerves

Spinal Cord Anatomy

Peripheral Nervous System (nerves outside of the CNS)•The PNS consists of 12 pairs (left and right) of cranial nerves originate from the brain and 31 pairs (left and right) of nerves are attached to the spinal cord

•Sensory (afferent)–all axons carry impulses from sensory receptors via the PNS to the CNS

•Motor (efferent)–all axons carry impulses via the PNS from CNS

•Mixed–a mixture of sensory and motor neurons that carry impulses via the PNS to and from CNS– most common type of nerve in the body

Sensory Division of the PNS

Sensory division •made of afferent neurons

–Somatic (body)–sensory neurons send APs from skin, skeletal muscles, and joints

–visceral sensory neurons send APs from organs within the abdominal and thoracic cavaties

Motor Division of the PNSMotor division •made of efferent neurons•control the action of effectors

–somatic motor neurons send APs to voluntary skeletal muscle –visceral motor neurons send APs to involuntary cardiac muscle, smooth muscle and glands

–a.k.a. the Autonomic Nervous System (ANS)–2 antagonistic (opposing) divisions

•Sympathetic•Parasympathetic

–the two divisions control the same effectors (with few exceptions) but create opposite responses in the effectors

Autonomic Nervous System-Visceral motor neurons of the PNS control the activity of involuntary effectors such as cardiac muscle, smooth muscle and glandular secretion affecting:

–heart rate–breathing rate–sweating–digestion–blood pressure

-Action potentials in these motor neurons are initiated in the medulla oblongata and the pons

–these motor neurons exit the brain by:•descending tracts of the spinal cord

–exit spinal cord via spinal nerves•cranial nerves

Efferent Pathways of the ANS

-Efferent pathways of the ANS consist of a two-neuron chain between the brain or spinal cord and the effector

-synapses between the neurons occur at ganglions

-The preganglionic begins in the CNS and extends along a nerve to the ganglion

–The postganglionic neuron extends from the ganglion to an effector organ

Organization of the Sympathetic

Division

Organization of the Parasympathetic

Division

Function of the Sympathetic Division-The sympathetic division is called the “fight or flight” system (mobilizes body in extreme situations) -activated when the body needs to expend energy•Involves E activities•exercise, excitement, emergency, and embarrassment•Promotes necessary changes during these activities

–increases heart rate, blood pressure, respiration rate, blood flow to skeletal muscles, glucose metabolism

-decreases the activity of and blood flow to the digestive system organs

-Its activity is illustrated by a person who is threatened

-the individual’s heart rate increases and the breathing

becomes deep-skin is cold and sweaty

-pupils dilate

Function of the Parasympathetic Division•The parasympathetic nervous system is called the “rest and digest” system

–activated when the body needs to conserve energy

•Involves the D activities –digestion, defecation, and diuresis (urination)

•Promotes necessary changes during these activities–decreases heart rate, blood pressure, respiration rate, blood flow to skeletal muscles, glucose metabolism –increases the activity of and blood flow to the digestive system organs

Its activity is illustrated in a person who relaxes after eating a meal

-Therefore maintenance activities-gastrointestinal activity is high

-skin is warm and pupils constricted

-most visceral organs are innervated by both sympathetic and parasympathetic nerves-Therefore, dynamic antagonisms that

precisely control visceral activitye.g. sympathetic increases heart rate,

respiration, and inhibits digestion while the parasympathetic decreases heart and

respiratory rates and allows for digestive system to be rid of wastes

Neurotransmitters of Sympathetic and Parasympathetic Divisions•The way the 2 divisions of the ANS can create opposite responses in the effectors that they control is by the release of different neurotransmitters onto the cells of the effectors

•All preganglionic neurons (sympathetic and parasympathetic) exocytose acetylcholine (ACh) onto postganglionic cells

–creating an AP in the postganglionic cell

•Sympathetic postganglionic cells release norepinephrine (NE) onto the effector•Parasympathetic postganglionic fibers release ACh onto effector

Efferent Sympathetic vs. Parasympathetic

Effects of Neurotransmitters of the Autonomic Nervous System

•The cells of each organ controlled by the ANS have membrane receptors to BOTH ACh and NE

–organs are dually controlled

-The response of the organ is determined by the identity of the neurotransmitter released

–the binding of ACh to its receptor will cause the effector to respond in one way

-the binding of NE to its receptor will cause the effector to respond in the opposite way

•The effect of ACh and NE on an effector can be either stimulatory or inhibitory (effector specific)

-NE increases heart rate, ACh decreases heart rate–NE decreases the secretion of saliva, ACh increases the secretion of saliva

Dual Control by the Sympathetic and

Parasympathetic Systems

BrainLeft Brain--Logic Details Facts Words Present/past Math/Science Knowing Reality

Right Brain-

- Feeling Big Picture Imagination Symbols Future Philosophy/Religion Spatial perception Risk Fantasy

Brain DysfunctionsTraumatic Brain Injuries

-Damage is caused not only at the site of a blow, but also by the effect of Ricocheting brain hitting the opposite side of the skull

1. Concussion

- slight brain injury

- maybe dizzy “seeing stars” or loss of consciousness, briefly

Levels of injury:

G-1: less than 15 min

G-2: greater than 15 min

G-3: loss of consciousness

Recovery (from sport):

G-1: 1 week

G-2: 2 weeks

G-3: 1 month

2. Contusion

- marked tissue damage

- if cerebral cortex is injured the individual may remain conscious

- but severe brain stem contusions always result in a coma lasting hours to a Lifetime

3. Inter Cranial Hemorrhage

- bleeding from ruptured vessels or cerebral edema (swelling of the brain due to inflammatory response to injury)

- individuals who are initially alert and lucid may begin to deteriortae neurologically later

Signs of a serious impact:

- headache that gets worse

-Confusion

-Disorientation

-Slurred speech

-Sleepiness

-Droopy eye

-amnesia

4. Cerebrovascular accident (strokes)

-3rd leading cause of death in the US

- blood circulating to the brain area is blocked (clot or ruptured blood vessel) - vital tissues dies

- brain area affected determined by observing patient’s symptoms

5. Cerebral Palsy

-One cause: temporary lack of oxygen at birth

- neuromuscular disability => voluntary muscles are poorly controlled because of brain damage

- 50% of patients have seizures

-some have mental retardation

- some have vision or hearing problems

Tracking down the problems:

1. Test reflexes - test of brain and spinal cord

2. Electroencephalography (EEG)

-electrodes placed on scalp to measure brain activity (impulses or brain waves)

- patterns vary depending on activity e.g. sleeping, coma

- lack of waves means brain death

3. CT Scan - 3D image from x-rays and the use if intravenously administered contrast dyes (high radiation)

4. MRI - Magnetic Resonance Imaging

-better image than a CT Scan

- uses a magnetic field therefore no radiation

5. PET - Positron Emission Tomography

-3D image

-uses gamma rays from a radioisotope that has a short half life

- may be used in conjunction with a CT Scan