Biology - The Nervous System

Central Nervous System

brain and spinal chord

Peripheral Nervous System

vast network of nerves

Reception

the stimulus must be detected

Transmission

the message passes along the neurons

Integration

incoming messages are sorted and processed and a response is decided upon

Response

carried out by effectors when stimulated by neurons

Neuron

a nerve cell

Sensory Neuron

takes a message from a sense organ to the CNS

Motor Neuron

takes a message from the CNS to a muscle or gland

Receptor

a cell or group of cells that detects a stimulus

Nerve Endings

connect sensory neurons to receptor cells and sense organs

Dendrites

fibres that carry impulses towards the cell body

Axons

carry nerve impulses away from cell bodies

Schwann Cells

produce the myelin sheath

Myelin Sheath

a fat-rich layer that insulates electrical impulses

Cell Body

contains a nucleus and cell organelles

• located outside the CNS (sensory neurons)

• located within the CNS (motor neurons)

Axon Terminals

branches formed by the splitting of an axon

Neurotransmitter Swellings

release chemicals that carry the impulse from one nerve cell to another

Ganglion

group of cell bodies located outside the CNS

Interneuron

carries information between sensory and motor neurons

Resting Neuron

neuron that is not carrying an impulse

Threshold

the minimum stimulus needed to cause an impulse to be carried in a neuron

All or Nothing Law

states that if the threshold is reached an impulse is carried, but if the threshold is not reached no impulse is carried

Refractory Period

a short time span after a neuron has carried an impulse during which a stimulus fails to cause a response

Synapse

a region where two neurons come in close contact

Synaptic Cleft

the tiny gap between the two neurons at a synapse

Myelin Sheath

speeds up the passage of an impulse

Nerve Impulse

• neurotransmitter swellings produce neurotransmitters such as ACh

• ACh diffuses across the synapse

• ACh causes the production of an electrical impulse at the other side where it is broken down by enzymes

Acetylcholine

ACh

Functions of Synapses

1. transmit impulses

2. control the direction of the impulse

3. prevent overstimulation of effectors

4. impulse can be blocked by certain chemicals

Cerebrum

• controls voluntary muscles

• receives impulses from sense organs

• intelligence

• memory

• language

• emotions

• judgement

• personality

Cerebellum

• controls muscular coordination

• balance

Medulla Oblongata

controls involuntary actions (e.g. breathing)

Thalamus

sends messages to different parts of the brain

Hypothalamus

controls internal environment of the body

Parkinson’s Disease

a nervous disorder caused by a lack of dopamine in the brain

Parkinson’s Symptoms

• trembling limbs

• a rigid body

• inability to walk properly

Parkinson’s Treatments

physiotherapy and drugs

Spinal Cord

carries impulses to and from the brain and controls many reflex actions

Sensory Neurons

enter spinal cord through dorsal roots

Dorsal Root Ganglion

contains the cell bodies of sensory neurons

White Matter

contains axons

Grey Matter

contains cell bodies and dendrites

Motor Neurons

emerge from the spinal cord through ventral roots

Reflex Action

an automatic, involuntary, unthinking response to a stimulus

Reflex Arc

the pathway taken by a nerve impulse in a reflex action

Route Along Reflex Arc

receptor → sensory neuron → spinal cord → interneuron → motor neuron → effector

Meninges

• protective tissue that surrounds the brain and spinal cord

• has three layers

Meningitis

infection of the meninges

Movement of Ions

how a nerve impulse is conducted along a neuron