Nervous System

Nervous system purpose

Detect stimuli (through receptors), converting it into nerve impulses → transmitted to the CNS for processing and coordinating a response

Sensory neuron

Transmits nerve impulses from the receptors in the body to Central Nervous System, located in ganglia

Relay neuron

Transmits nerve impulses from the sensory to motor neuron. Found in central nervous system. Found in CNS.

Structure: Short dendrons, axon unmyelinated

Motor neuron

Conducts impulses from CNS to the effectors, such as muscles and glands. Found in grey matter of CNS.

Effectors

Produce an appropriate response

Neurons

Responsible for transmitting nerve impulses in the nervous system

Axon

Very elongated nerve fibre. Transmits impulses away from the cell body → other neurons /cells of an effector.

Dendron

A nerve fibre that transmits nerve impulses towards the cell body.

A dendron usually branches into more dendrites, which receive impulses from other neurons.

Myelin Sheath

Axon of some neurons is covered by myelin, made up of mainly lipids, that insulates the axon.

[Myelinated neurons]

Schwann cells deposit the myelin by growing round and round the axon.

Node of Ranvier

Region where the myelin sheath is absent. Allow nerve impulses to jump from node to node, speeding up rate of transmission.

! saltatory conduction

Motor end plate [motor]

Formed where the end branch of an axon comes into contact with the muscle fibre.

Impulses are transmitted across the motor end plate by chemicals, which stimulate the muscle.

Synapse

A synapse is junction between two neurons or between a neuron and an effector (e.g. muscle or a gland).

Synapse process

1. Nerve impulses transmitted between neurons across a synapse

2. When a nerve impulse arrives at a synapse, neurotransmitters are released into the synaptic cleft

3. Neurotransmitters diffuse across cleft, bind to receptors on the post-synaptic membrane

4. Ion channels in post-synaptic membrane open

5. Nerve impulse subsequently generated in post-synaptic neuron

Neurotransmitters

Send signals across a synapse; chemicals like dopamine

Reflex action

An immediate response to a specific stimulus without conscious control, e.g. pain withdrawal reflex.

Blinking

Blinking: When something approaches your eye, like a speck of dust or a finger, your eyelids automatically close to protect the eye. Cranial reflex.

Shivering

Shivering: This is a reflex response to cold temperature, generating heat through muscle contractions. Spinal reflex.

Importance of reflex

1. Make involuntary adjustments to changes in external env.

2. Enable body to respond to dangers

3. Control internal environment

Reflex arc

Shortest pathway by which nerve impulses travel from receptor → effector