Chapter 22 The Human Nervous System

The Nervous System controls body movements and many internal functions.

The nervous system is divided in two

Central nervous system - brain and spinal cord

Peripheral nervous system - sense organs and nerves that branch off the central n.s.

Neurons are cells that can transfer an electrochemical impulse

Parts of the neuron:

Cell body - nucleus, organelles and cytoplasm - largest part of neuron

Dendrites - shorter branches from the cell body that carry impulses to cell body

Axons - longer branch that carries impulses away from cell body

How does an impulse move from axon of one neuron to the dendrite of the next neuron?

The impulse must transmit across a very short space called a synapse.

Impulse travels along axon to end where vesicles contain neurotransmitters.

Impulse directs vesicles to membrane.

Vesicles release neurotransmitters across synapse to dendrite of next neuron.

Impulse travels along neurons until it reaches the effector. Effector is the part of the body that

responds to the impulse. (muscle, gland)

A reflex is an immediate, inborn (not learned), involuntary response to a stimulus.

A stimulus is a change in the environment that causes your body to react.

A reflex arc is a series of neurons that receive a stimulus then cause the body to react to it.

The sensory neuron is responsible for sensing the stimuli and carrying the impulses to the

central nervous system.

When the impulse reaches the spinal cord, the interneuron then carries the impulse to the

motor neuron.

The motor neuron then carries the impulse from the spinal cord to the effector and moves the

muscle. All this action is involuntary and happens before impulses get to the brain and knows

what happened.

The Brain

12 billion neurons

12 pairs of cranial nerves carry impulses to head, neck and internal organs.

Brain 3 main parts - Cerebrum, Cerebellum, and Brain Stem

Cerebrum - largest part of the brain divided into 2 hemispheres each with 4 lobes

Cerebral cortex is the outside layer responsible for conscious activities

Frontal Lobes - body movements, personality, verbal communication

Parietal Lobes - sensations like pain, pressure, temperature

Temporal Lobes - receive impulses from ear and interpret them as sound

Occipital Lobes - receive impulses from eyes and interpret them as sight

Cerebellum - monitoring and controlling bodily movements without thinking about them.

Brain stem - helps control breathing, heartbeat, blood pressure, coughing, sneezing and

swallowing.

Spinal cord is continuous with brain stem and extends down the back. It relays impulses

between brain and the rest of the body.