The Nervous System

Two Divisions:

n The Central Nervous System

n Spinal cord and Brain

n Peripheral Nervous System

n Nerves of body

General Functions

n Sensory – receives information

n Motor – control of effector organs

n Integration – control

Nervous System structure

n Neurons

n Spinal cord

n Brain

**see overheads for details

The Brain

n Forebrain (Cerebrum)

n Largest part

n 2 spheres, controls voluntary action

n Outer surface is called the cortex (gray matter)

n Inner surface is called the medulla (white matter)

n Spheres are divided into lobes; each lobe has a specific function (right side = artistic; left side = language, math, logic)

Brain Cont.

n Hindbrain (cerebellum)

n Located below the forebrain

n Helps in muscle activity control, balance

n Involuntary

n If damaged: lack of coordination, weak muscles; simple tasks become difficult

Brain cont.

n Brain stem

n Connects the brain to the spinal cord

n Entry and exit place of all information

n Contains the medulla oblongata (breathing, blood pressure, swallowing)

n Contains the R.A.S. (reticular activating system): controls the alertness of brain

n Contains the Pons: bridge between the cerebral cortex and the cerebellum

n Contains the midbrain: involved in hearing and vision

Connections Between Neurons

n Neurons Lie axon to dendrite

n They don’t Touch

n Junction/space between them is known as a synapse

n The impulse must jump across the gap, but how?

How?

n 1.Impulse reaches the end of the axon

n 2. Vesicle with neurotransmitter on the inside

n 3.Vesicle fuses with membrane

n 4. Neurotransmitter diffuses across synapse and binds with receptor on dendrite

n 5. Neurotransmitter released into synapse

n Impulse is spread

Peripheral Nervous System

n Made up of all the nerves that carry messages to and from the central nervous system which relays the message to a motor neuron that carries the impulse to the muscle

n Two divisions:

n Somatic

n Autonomic

Somatic Nervous System

n Found in clusters along the spinal column.

n Contain both sensory and motor axons

n Relay information mainly between your skin, the CNS and the skeletal muscles.

n Voluntary

Reflexes in the Somatic Nervous System

n Sometimes reaction is automatic and unconscious- REFLEX

n Impulse travels directly to the spinal column and back to the muscle

n Brain is aware of the reflex only after it occurs.

Autonomic Nervous System

n Scary situations, the ANS takes over!

n Carries impulses from the CNS to internal organs

n Produces involuntary responses

n Sympathetic

n parasympathetic

Sympathetic

n Controls many internal functions during times of stress

n Releases hormone of fight or flight

n Adrenalin

Parasympathetic

n Controls many of the body’s internal functions

n Controls body when relaxing

n Reaction depends on action of sympathetic

The Senses

Sensing Chemicals

n We smell and taste chemicals that interact with receptors in our nose and mouth

n In your nose it is hair-like nerve endings in the upper portion of your nose

n Impulse then goes to the olfactory nerve and signals the brain as the interpreted odor.

n Taste and smell are closely linked

Taste

n You taste when chemicals dissolved in saliva contact chemicals dissolved in saliva.

n These chemicals then contact sensory receptors on your tongue-Taste Buds

n Taste bud sends signal to cerebrum and we say yummy!

n Divided into four basic categories

n Sour, salty, bitter, sweet.

Taste Continued

n Certain regions are stronger on different parts of the tongue

n Bitter-Back

n Sour-Sides

n Sweet/Salty-Tip

Sensing Light

n Retina is stimulated by receptors that are sensitive to light

n Enters pupil, focused by lense, strikes retina

n Retina

n Rods, and cones

• Rods-dim light

• Cones-sharp vision and bright light

• Optic nerve leads to the Brain

Hearing

n Sound travels in waves

n Sound travels down the ear canal and causes eardrum to vibrate

n Strike three small bones and cause liquid to vibrate at same wave as the sound.

n Triggers hair cells that send response to the brain

Balance

n Inner ear liquid tells us if we are balanced

n Liquid in semicircular canals sends impulses to the brain

Touch

n Receptors in the dermis/skin

n Changes in temp/pressure/pain

n Usually concentrated in certain areas