Nervous System Chapter 9. Introduction to the NS Neurons – nerve cells Neurons – nerve cells...

Nervous System

Chapter 9

Introduction to the NS Neurons – nerve cells Nerve impulses – electrochemical

changes which transmit information Neurons consist of:

• Cell body – rounded area• Dendrites – extensions that receive nerve

impulses• Axons – extensions that send nerve impulses

(usually has only one) Nerves – bundles of axons Neuroglial cells – provide physical

support, insulation, and nutrients for neurons

Groups

Central nervous system – consists of brain and spinal cord

Peripheral nervous system – consists of nerves that connect the cns to the other body parts

Functions:• Sensory• Integrative• Motor

Sensory Function

Sensory receptors are found at the ends of peripheral neurons gather info. by detecting changes inside and outside the body.

Monitor such things as light, sound, temperature, oxygen level

Integrative Function

Nerve impulses from sensory receptors are transmitted to the cns

Signals are brought together, creating sensations, adding to memory, or helping produce thoughts that translate sensations into perceptions

Motor Function

Impulses from cns to responsive structures called effectors • Examples: muscles that contract, glands

that secrete Somatic nervous system – motor

functions that are consciously controlled

Autonomic nervous system – motor functions that are involuntary

Dimethylmercury Poisoning

Clings to brain neurons, destroying them

Neuroglial cells overgrow

Neuroglial Cells Microglial – scattered throughout cns; support

neurons and phagocytize bacterial cells and cellular debris

Oligodendrocytes – align along nerve fibers; provide insulating layers of myelin around axons within the cns

Astrocytes – found between neurons and blood vessels; provide structural support; help regulate conc. of nutrients and ions within the tissue; form scar tissue

Ependymal cells – form an epithelia-like membrane that covers specialized brain parts; forms inner linings

Schwann cells – form a myelin sheath around axons of the pns

Gliomas

Fast-growing brain tumors Consist of rapidly dividing neuroglia

Neurons Cell body

• Granular cytoplasm• Cell membrane• Organelles (mitochondria, lysosomes, neurofibrils)• Nissl bodies (similar to rough ER)

Dendrites• Short and highly branched• Main receptive surfaces

Axons• Conducts nerve impulses away from the cell body• Usually a single structure• Surrounded by Schwann cells to form a myelin sheath• Spaces in between are called nodes of Ranvier

Neural stem cells found in the hippocampus

Structural Classification of Neurons

Multipolar – one axon; many dendrites; lie within the brain or spinal cord

Bipolar – one axon; one dendrite; lie within eye, nose, and ears

Unipolar – one axon that branches into two; one assoc. with peripheral body part and the other enters the brain or spinal cord

Functional Classification of Neurons

Sensory neurons – carry nerve impulses from peripheral body parts into the brain or spinal cord

Interneurons – transmit impulses from one part of the brain or spinal cord to another

Motor neurons – carry nerve impulses out of the brain or spinal cord to effectors

Cell Membrane Potential

Surface of a cell membrane is usually electrically charged or polarized with respect to the inside

Polarization due to an unequal distribution of positive and negative ions between sides of the membrane

Distribution of Ions

Greater conc. of Na+ outside cell Greater conc. of K+ inside cell

Resting Potential of Neuron Resting membrane

more permeable to K+ than to Na+

K+ leaves faster than Na+ enters

There exists a potential difference of charges in a resting nerve cell between the region inside the membrane and outside the membrane

Potential Changes

Depolarization – resting potential decrease (inside becomes less negative than outside as Na ions leave)

This produces a local current If additional stimulation arrives before the

effect of the previous stimulation subsides, the change in potential is still greater (summation)

Threshold potential is reached as a result of summated potentials

Action Potential

At the threshold potential, permeability suddenly changes at the trigger zone (portion of axon where impulse begins) allowing Na+ in

Cell becomes depolarized and repolarized as K+ enter once more

Action potential – rapid sequence of depolarization and repolarization

Agh!

Local anesthetic drugs decrease membrane permeability to sodium ions

It interrupts impulses from passing through the affected region and reaching the brain

Prevents the sensations of touch and pain

Impulse Conduction

Myelinated sheath prevents almost all ion flow through the membrane it encloses

Nodes of Ranvier between Schwann cells interrupt the sheath

Action potentials occur at these nodes Speed of nerve impulse conduction is

proportional to the diameter of the axon (greater diameter=faster impulse)

All-Or-None Response

If a neuron responds at all, it responds completely

Conduction occurs when a stimulus of threshold intensity or above is applied

All impulses carried on that axon are of the same strength

Greater intensity=more impulses per second

Events leading to the conduction of a nerve impulse

1. Neuron membrane maintains resting potential

2. Threshold stimulus is received3. Sodium channels in the trigger zone

of the neuron open4. Sodium ions diffuse inward,

depolarizing the membrane5. Potassium channels in the

membrane open

6. Potassium ions diffuse outward, repolarizing the membrane

7. The resulting action potential causes a local bioelectric current that stimulates adjacent portions of the membrane

8. A wave of action potentials travels the length of the axon as a nerve impulse

Flipbook

Create a flipbook illustrating and describing the events leading to the conduction of a nerve impulse

Must be labeled, colored, and include a short description

The Synapse

Nerve impulses travel along nerve pathways

The junction between any two communicating neurons is called a synapse

Types of Nerves

Afferent fibers bring sensory information into the CNS

Efferent fibers carry impulses from the CNS to effectors (muscles or glands)

Reflex Arc Type of nerve pathway Reflexes are automatic subconscious

responses to stimuli within or outside the body

Help maintain homeostasis by controlling heart rate, breathing rate, blood pressure, and digestion

Knee-jerk reflex helps maintain upright posture

Withdrawal reflex occurs when a person unexpectedly touches a body part to something painful

Meninges

Membranes that lie between bone and soft tissues of CNS

Dura mater • outermost layer• composed of tough, white, fibrous

connective tissue• contains many blood vessels and nerves

Arachnoid mater• thin, weblike membrane• Lacks blood vessels• Lies between the dura and pia maters• Spreads over the brain and spinal cord

Pia mater• Very thin• Contains blood vessels that nourish underlying

cells of the brain and spinal cord• Hugs the surfaces of organs

Spinal Cord

Slender nerve column that passes downward from the brain into the vertebral column

Consists of 31 segments, each of which gives rise to a pair of spinal nerves

Conducts nerve impulses Serves as a center for spinal reflexes

Brain

Composed of about 100 billion multipolar neurons

Weighs about 3.5 lbs.

If all the cells were laid end-to-end, they would cover 600 miles

Cerebrum

Consists of left and right hemispheres

Deep bridge of nerve fibers called the corpus callosum connects the cerebral hemispheres

A layer of dura mater separates them Gyri – ridges found on surface Sulcus – shallow groove Fissure – deep groove

Lobes of Cerebrum

Frontal – forms anterior portion of each hemisphere

Parietal – posterior to the frontal lobe

Temporal – lies below frontal and parietal lobes

Occipital – forms posterior portion of each hemisphere

Cerebrum cont.

Cerebral cortex – outermost portion of the cerebrum composed of a thin layer of gray matter

Just beneath the cerebral cortex is a mass of white matter that makes up the bulk of the cerebrum

Provides higher brain functions Stores information that comprises

memory and utilizes it to reason

Functions of the Cerebrum

1. Motor area for voluntary muscle control

2. Motor speech area3. Auditory area4. Cutaneous sensory area5. General interpretative area6. Visual area

Hemisphere Dominance

Both hemispheres participate in basic functions

In most persons, however, one side of the cerebrum is the dominant hemisphere, controlling the ability to use and understand language

Left hemisphere is dominant in more than 90% of the population

Non-dominant hemisphere controls emotional and intuitive thinking

Cerebrospinal Fluid

Secreted by choroid plexuses found in the pia mater

Completely surrounds the brain and spinal cord

Organs float Support and protection is provided by

absorption of forces

Diencephalon

Located between the cerebral hemispheres and above the midbrain

Composed largely of gray matter Thalamus within the diencephalon relays

sensory impulses from other parts of the nervous system to the cerebral cortex

Hypothalamus lies below the thalamus and maintains homeostasis by regulating a variety of visceral activities and by linking the nervous and endocrine systems

Brainstem – bundle of nervous tissue that connects the cerebrum to the spinal cord• Midbrain – contains bundles of myelinated

axons that join lower parts of the brainstem and spinal cord with higher parts of the brain

• Pons – rounded bulge on the underside of the brainstem; relays impulses to and from the medulla oblongata

• Medulla oblongata – relays impulses, controls vital visceral activities, and reflexes

Cerebellum

Large mass of tissue located below the occipital lobes of the cerebrum and posterior to the pons and medulla oblongata

Consists of two lateral hemispheres Reflex center for integrating sensory

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

Helps maintain posture

Peripheral Nervous System (PNS)

Consists of nerves that branch out from the CNS and connect it to other body parts

Subdivided into the somatic and autonomic nervous systems

Somatic Nervous System

Cranial and spinal nerves Connect the CNS to the skin and

skeletal muscles Oversees conscious activities

Cranial Nerves

Autonomic Nervous System

Functions independently and continuously without conscious effort

Regulates the actions of smooth muscles, cardiac muscles, and glands

Responds to emotional stress and prepares the body to meet the demands of strenuous physical activity

Pictionary!!!

Choose a card from the deck. Draw a picture on the board for your team members to guess before time runs out. You will have one minute to complete your drawing and have your team guess before the chance goes to the other team. You may not use hand motions or any sound effects.

Disorders/Diseases

Attention Deficit-Hyperactivity Disorder • affects 3-5 percent of all American

children • interferes with a person's ability to stay

on a task and to exercise age-appropriate inhibition

• causes

Alzheimer's disease • age-related, non-reversible brain disorder that

develops over a period of years • Symptoms

behavior and personality changes decline in cognitive abilities such as decision-making

and language skills problems recognizing family and friends ultimately leads to a severe loss of mental function

and death• Cause

Plaques caused by protein buildup

Dementia• impaired intellectual functioning that interferes

with normal activities and relationships • lose their ability to solve problems and

maintain emotional control, and they may experience personality changes and behavioral problems, such as agitation, delusions, and hallucinations

• Caused by Alzheimer’s disease, vascular dementia, Lewy body dementia, frontotemporal dementia, Huntington’s disease, and Creutzfeldt-Jakob disease

Coma• profound or deep state of unconsciousness • may occur as a complication of an underlying

illness, or as a result of injuries, such as head trauma

• Although individuals in a persistent vegetative state may appear somewhat normal, they do not speak and they are unable to respond to commands

• rarely lasts more than 2 to 4 weeks

Meningitis and Encephalitis• inflammatory diseases of the

membranes that surround the brain and spinal cord and are caused by bacterial or viral infections

• sudden fever, headache, vomiting, heightened sensitivity to light, stiff neck and back, confusion and impaired judgment, drowsiness, weak muscles, a clumsy and unsteady gait, and irritability

Epilepsy• clusters of neurons in the brain

sometimes signal abnormally• strange sensations, emotions, and

behavior or sometimes convulsions, muscle spasms, and loss of consciousness

• Illness, brain damage or abnormal brain development can lead to seizures

Parkinson's Disease• result of the loss of dopamine-producing

brain cells• tremor, or trembling in hands, arms,

legs, jaw, and face; rigidity, or stiffness of the limbs and trunk; bradykinesia, or slowness of movement; and postural instability, or impaired balance and coordination