NERVOUS SYSTEM

Its function is to control and co-ordinate the parts of the body.

CENTRAL NERVOUS SYSTEM(CNS)

PERIPHERAL NERVOUS SYSTEM

(PNS)

BRAIN receives and sends out messages.

SPINAL CORD connects the brain to the rest of the body.

CRANIAL NERVES carry messages directly to and from the brain.

SPINAL NERVES carry messages to and from the spinal cord.

Coordinating center for incoming and outgoing information

Carry info. between organs such as skin, heart, eyes, ears and the CNS.

Peripheral Nervous System

Somatic Nervous System

• Sensory and motor neurons under conscious control

VOLUNTARY

e.g. controls skeletal muscles

Autonomic Nervous System

• Motor neurons that function without conscious control

INVOLUNTARY

e.g. controls heart rate, blood pressure, digestive muscles, breathing

NERVE CELLSThere are two types:

1. Glial cells – non-conducting / important for structural support and Schwann cells make myelin

2. Neurons - Specialized cells that can carry electro-chemical messages called NERVE IMPULSES

Neurons can be classed according to function.

•Sensory neurons

•Interneurons – link neurons

•Motor neurons

Direction of impulse

Receptor Dendrite

Cell body

Axon

Branches forming synapse

These sense and relay info. from the environment to CNS•Baroreceptors (detect pressure)•Chemoreceptors (detect chemicals)•Photoreceptors (detect light)•Osmoreceptors•Thermoreceptors

SENSORY NEURONS

MOTOR NEURONES

These carry impulses from the CNS to an EFFECTOR (a muscle or a gland or an organ).

Direction of impulse

DendritesCell body

AxonNerve endings on a muscle

Both sensory and motor neurons are very long (up to 1m in a human). This helps to reduce the synapses (connections) needed.

Neurons can also be classified structurally

• Several dendrites, one axon, found in brain and spinal cord

• Single dendrite, single axon, found in inner ear, retina of eye and olfactory area of brain

• Dendrite and axon are fused and extend from cell body, found in peripheral nervous system

The importance of myelin

Many neurons have axons that are covered in a fatty substance called myelin. This insulates the axons so it stops impulses jumping from one

axon into others next to it. The myelin sheath also increases impulse speeds.

Direction of impulse

Myelin sheath

NERVES

NERVE CELLS (FIBRES)

NERVE

A nerve is a bundle of nerve fibres (cells).

Most nerves carry a mixture of sensory and motor fibres.

SYNAPSESNerve impulses can travel at up to 100m per sec but when they reach the end of a cell they have to cross a gap called a SYNAPSE.

IMPULSE IMPULSE

Impulse arrives at the end of first neuron.TRANSMITTER chemical is released from vesicles.TRANSMITTER diffuses across the gap

When TRANSMITTER reaches second neuron it starts a new impulse.

The synapse

The gap between neurones is called a synapse. Messages are sent across this gap using chemical messengers.

End of neurone

(Axon terminal)

Chemical is released by one neurone and detected by the next

Impulse travels along axon to the terminal

An impulse travels through the neurone

Serotonin

Normal functions– Emotions– Judgment– Sleep

Imbalances

– Depression

– Suicidal behavior

– Anxiety

– Impulsive behavior

– Eating disorders

Glutamate/Glutamate/GABAGABA

Normal functions

• Involved in most facets of brain function

Imbalances

Memory disturbances

Sleep disturbances

Anxiety

Dopamine

Normal functions– Mood

– Movement

– Memory

Imbalances– Movement disorders

– Schizophrenia

– Addiction

EndorphinsEndorphins

Normal functions

• Relieve pain

• Induce euphoria

NERVE PATHWAY

STIMULUS RECEPTOR

SENSORY NEURON

C.N.S. (interneurons)

MOTOR NEURON

EFFECTORRESPONSE

REFLEXES

These reactions are:-

Fast

Automatic

Unlearned

Do not involve the brain

Often designed to protect the body

Examples :-

COUGHING Removes particles from breathing system

PUPIL REFLEX

Automatically adjusts the eye to light intensity

WITHDRAWAL REFLEX

Removes arm or leg from a painful stimulus to prevent damage.

Motor neurone

Sensory neurone

Effector (Biceps)

Receptor in skin

Spinal cord

REFLEX ARC

The path taken by an impulse during a reflex eg Withdrawing hand from a painful stimulus.

Reflex arcFinger touches hot object

Receptor in skin detects stimulus

Sensory neurone sends impulse to spinal cord

Motor neurone picks up impulse from sensory neurone and sends impulse to the effector

Effector (muscle) moves hand away from dangerGap between

neurones is called synapse

REFLEX ARC IN SPINAL CORD

Grey matter

White matter

Sensory neuron

Motor neuron

Interneuron Synapse

Dorsal root of spinal nerve

SEQUENCE OF EVENTS

1. Skin of hand touches a hot surface.

2. Temperature receptors in the skin start an impulse3. Impulse travels up the spinal nerve of the arm in a sensory neuron.

4. Impulse passed to relay neurone in spinal cord5. Impulse travels down the spinal nerve of the arm in a motor neuron.

6. Impulse causes BICEPS muscle to contract bending the arm and pulling the hand away

NB Although the brain is informed it does not have time to stop the reaction.

The reflex is fast because:-

The impulse does not need to travel through the brain so it only involves two synapses.

Synapses delay a reaction because of the time taken for transmitter to diffuse across the gap between neurones.