2.83 - 2.85

2.83 recall that the central nervous system consists of the brain and spinal cord and is linked to sense organs by nerves

Sensory Neurone

2.84 understand that stimulation of receptors in the sense organs sends electrical impulses along nerves into and out of the central nervous system, resulting in rapid responses

Cells are wrapped around the axon (schuann cells). This takes place all the way down the sensory axons and motor axons.

 

Signals are sent through the nervous system in the form of electro-chemical impulses. Sensory neurones (nerve cells) carry signals to the CNS. Motor neurones send out information from the brain, controlling how the body responds. Relay neurones connect other neurones together.

Myelination

The axons are covered with myelin sheath. This makes the transfer of information faster because they jump down the nodes of Ranvier. Myelination takes place in sensory and motor neurons, which increases speed of conduction.

The myelin sheaths are white matter. The ends that are not covered in myelin are known as the grey matter. The relay neuron is grey. Grey matter is where nerves come together and make connections (synapse). Grey matter has lateral input while white matter has vertical input (up and down the nerves – nerve cells that are myelinated).

Learning a new skill – e.g. golf, piano

Repeat the same action à Reinforce pathways by myelinating it à Other pathways disappear, the nervous system is restructured à sleep à your brain develops myelinated sheath and modifies etc.

2.85 describe the structure and functioning of a simple reflex arc illustrated by the withdrawal of a finger from a hot object

The simplest type of response is a reflex. Reflexes are rapid, automatic responses to a specific stimulus that often protects you e.g. blinking, sneezing, withdrawing finger from fire.

VOLUNTARY Stimuli à Receptor à Co-ordinator (CNS – goes through the brain, 12 cranial nerves enter the brain) à Effector à Response

INVOLUNTARY Reflex – Stimuli à Receptor (fingertip) à Sensory neuron à Coordinator (CNS – spine) à Motor neuron à Effector (muscles) à Response (movement)

Reflexes are there to protect you from damage. You want to minimise the reaction time as much as possible. The information goes to the spine. The sensory neuron is directly connected to relay nerve which is connected to the motor nerve. Since it is a fixed decision, whether it goes through the brain or not, the output will be the same.