Motor neurons

(efferent)

Motor neurons carry messages away from the brain and spinal cord to the organs and muscles in the body.

A motor neuron has a cell body with many dendrites branching off it. These dendrites have a large surface area in order to connect with other neurons and carry nerve impulses towards the cell body.

The axon then carries the nerve impulse away from the cell body. Surrounding the axon are special cells known as Schwahn cells that wrap around the axon to form an insulating layer called a myelin sheath. At its end the axon divides into a number of branches known as synaptic terminals. These synaptic terminals do not actuall touch the next neuron; there is a small gap between the synaptic terminals and the dendrites of the receiving neuron known as a synapse.

Sensory neurons

Sensory neurons carry messages from the receptors in the body to our brain and spinal cord. Receptors such as our sense organs, muscles, skin or joints detect physical and chemical changes in the body and relay these messages via sensory neurons to the brain or spinal cord.

Interconnecting (relay) neurons are found only in our visual system, brain and spinal cord. These neurons receive messages from the sensory neurons and pass theses messages either to other interconnecting neurons or to motor neurons. The interaction of these three types of neurons can be seen in a diagram of a reflex arc.

Synaptic transmission

Action potential: electrical impulse along a neuron

Synapse: The gap between the end of one neuron and the dendrites of the next neuron

Neurotransmitter: a chemical substance released from a synaptic vesicle that affects the transfer of an impulse to another nerve or muscle

The cerebrum

The cerebrum has an outermost layer known as the cerebral cortex. The cortex appears grey because of the location of cell bodies- which is why it is known as grey matter. Beneath the cortex lie myelinetated axons which appear as white- hence it is known as white matter. Each of our sensory systems sends messages to and from this cerebral cortex.

The motor area

This is located in the parietal lobe and is responsible for controlling our voluntary movements. Movements on the right side of the body are controlled by the left hemisphere and vice versa. Therefore damage to the motor cortex results in impaired movements.

The somatosensory area

This is also located in the parietal lobe and separated from the motor area by the central sulcus lies the somatosensory area which responds to heat, cold, touch, pain and our sense of body movement. The amount of somato sensory area associated with a particular part of the body is related to its use and sensitivity.

name the different lobes

1. The frontal lobe – the location for awareness of what we are doing within our environment

2. The parietal lobe – location for sensory and motor movements

3. The temporal lobe – location for auditory ability and memory acquisition

4. The occipital lobe – location for vision

Autonomic nervous system (ANS)

Function: controls the functions of blood vessels, glands and the internal organs of the body (e.g. bladder, stomach and heart)

It mainly operates automatically i.e. without conscious control

The ANS is sub-divided into the sympathetic and parasympathetic nervous system.

The sympathetic nervous system

• Prepares the body for fight or flight

• During fight or flight, the sympathetic nervous system will divert blood from the stomach to the muscles, increase heart rate and breathing rate and dilate pupils

The parasympathetic nervous system

• Supports normal body functions, conserving and storing bodily energy

• It also reduces the effects of body changes caused by the sympathetic nervous system

• This involves reducing heart rate and breathing and contracting pupils.

sympathetic and parasympathetic functions

made up of a number of glands that secrete hormones into the bloodstream

Hormones travel through a bloodstream and affect different body organs.

The endocrine system provides a means of communication to the nervous system.

The chemical structure of hormones is very similar to that of the neurotransmitters found in the synaptic vesicles of neurons. E.g. the hormone adrenaline is chemically the same as epinephrine (a neurotransmitter).

located immediately above the kidneys. They secrete a number of hormones. The most important for psychology is adrenaline which is involved in the fight or flight response. Adrenaline has been linked to stress reactions:

In stress situation, 2 chemical reactions take place

1. Fast chemical response – stimulates the sympathetic nervous system which instructs the adrenal gland to produce adrenaline, thus giving an ‘adrenaline rush’

2. Slow chemical response – the hypothalamus stimulates the pituitary gland which then instructs the adrenal gland to produce the hormone cortisol. This inhibits reproductive features and allows glucose to be released into the bloodstream to provide energy.

The human nervous system is divided into two main sub-systems:

• The central nervous system which consists of the brain and spinal cord

• The peripheral nervous system which consists of millions of neurons that carry messages to and from the central nervous system. These neurons are known as motor, sensory and interconnecting neurons.