C H A P T E R 2

Nervous System

Input

Output

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Neuron

Nerve cell

Allows information to travel throughout the body to various destinations

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Receptive Segment

Transmissive Segment

Conductive Segment

Cell Body

Myelin sheath

Motor end plate

Dendrites: receive message

Terminal ending on muscle: sends off message to adjacent neuron

Axon: transmits

message to terminal ending

Myelin sheath: fatty covering or insulator

Skipping of the impulse allowing faster

conduction

Types of Neurons

Sensory neurons

Carry signals to the spinal cord & brain

Motor neurons

Carry signals from the spinal cord & brain

Interneurons

Originate and terminate in CNS

Connect afferents and efferents in CNS

Process incoming signals

Pass response impulse on to motor neurons

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Types of Neurons cont.

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The Neuron’s Function

Receptive segment (dendrites) Receives continuous synaptic input

(chemical) from other neurons

Conductive segment (axon) Conduction of neural information in the

form of nerve impulse (electrical)

Transmissive segment (axon terminals) Converts electrical nerve impulse to

chemical form (neurotransmitter) and sends it off to dendrites

Receptive

Transmissive

Conductive

Sensory – monitors environment through presence of receptors

Integration – interpretation of sensory information (information processing)

Motor – response to information processed through stimulation of effectors

The Nervous system has three major functions:

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CNS

Brain & Spinal Cord

Control center

PNS

Connects CNS with the rest of the body

Nervous System Divisions

Nervous System

CNS

PNS

Sensory/Afferent

Motor/Efferent

Somatic

Autonomic

Peripheral Nervous System

Peripheral Nervous System

12 pairs of cranial nerves

31 pairs of spinal nerves

8 pairs of cervical nerves

12 pairs of thoracic nerves

5 pairs of lumbar nerves

5 pairs of sacral nerves

1 pair of coccygeal nerves

Spinal Nerve Attachments

Spinal Nerve Attachments (Cont)

CNS: Spinal Cord

Consists of neurons through the holes in the vertebrae

Holes form a continuous canal

Protected by vertebrae, ligaments & cerebrospinal fluid that fills the canal

Cord connects to the brain at the brainstem through the foramen magnum

Functions of Spinal Cord

1. Intermediate nerve center between spinal nerves & brain

Interneurons integrate messages from various sensory impulses

Interneurons can add commands to the msg from the brain

Functions of Spinal Cord (Cont)

2. Major center for reflexes

Interneurons can match incoming sensory impulses directly with motor commands without brain intervention

Grey Matter White Matter

Interneurons, sensory & motor nerve fibers

Grey colour: cell bodies of interneurons and moter neurons

Bundles of axons

White colour: myelin sheaths

Structure of Spinal Cord

Ventral (anterior)

Dorsal (posterior)

White Matter of Spinal Cord

Ascending fibers: sensory information from sensory neurons of body up to brain

Descending fibers: motor instructions from brain to spinal cord

Descending Fibers: Voluntary Movements

Pyramidal tract Function: Transmit

voluntary movement Originates: Motor Cortex and

travels through pyramids of medulla

Fast tract

Extrapyramidal tract Function: Transmit postural

adjustments & learned reflexes

Travels outside pyramids of medulla

Slower pathway: more interneurons: add fine details

CNS: The Brain

Primarily composed of interneurons

Primary functions parallel the 3 types of neurons:

Sensory function

Association function

Motor function

Cerebrum

Diencephalon

Brain stem

Cerebellum

Regions of the Brain

Brainstem

Medulla

Pons

Midbrain

Reticular Formation

Medulla

Controls breathing, talking, swallowing, maintenance of BP

L&R sides= pyramids

At medulla nerve fibers cross the body before entering the spinal cord

Pons

Links higher brain centers to cerebellum

Relay point between brain & spinal cord

Influence breathing

Midbrain

Smallest division of brainstem

Neck & head reflexes

Elementary forms of seeing & hearing

Reticular Formation Formation

•Located in center of brainstem •Net-like neural network •Alerts the higher brain centers On incoming info •Maintains consciousness and alertness

Diencephalon

Thalamus

Hypothalamus

Thalamus

Relay station between higher & lower centers

Integrate info gathered from all senses

Hypothalamus

Regulatory center for activities of the autonomic system

Command center for complex mood & anger, aggression, fear, pleasure, thirst, hunger, sexual behaviour...

Cerebellum

General control & coordination center for movement

Monitor balance, posture & joint movements

Memory capacity for well learned skills

Cerebrum: Cortex Lobes

Frontal Lobe

Premotor Cortex

Motor Cortex

Parietal Lobe

Sensory Cortex

Sensory Association Cortex

Temporal Lobe

Auditory cortex

Auditory association cortex

Occipital Lobe

Visual cortex

Visual association cortex

Sensory Cortex

Touch Proprioception

Sensory Association Cortex

Receive info from

sensory cortex,

visual association cortex &

auditory association cortex

Integrates info and interprets its meaning by comparing it to your past experiences

Visual Cortex

Visual Association Cortex

Stores visual memory and permits perception of sight

Auditory Cortex

Auditory Association Area

Stores auditory memory and permits perception of sounds

Pre-Motor Cortex

Interpret Meaning of Situation

Decide whether to take action or not

Design plan of action

Motor Cortex

Receives action plan from pre-motor cortex

Generate commands for muscle activity