The Nervous System

Nervous system is divided into 2 parts: Central Nervous System (CNS) Brain and Spinal Cord Peripheral Nervous System (PNS) Nerves that carry messages between CNS & rest of body.

To make the correct response to a stimulus, 4 processes are involved Reception, a stimulus is detected, this is the function of neurons & sense organs Transmission, msg passes along neurons Receptors -> PNS -> CNS CNS -> PNS -> Effectors (muscles) Integration, Msgs are sorted and processed and a response decided upon. Response, carried out by effectors when stimulated by neurons

Neurons Is a nerve cell, specialised to carry info 3 types of neurons Sensory To Brain Motor To muscles Interneuron's Between Sensory & Motor

Structure of Neurons Neurons vary in size, neurons in the brain are tiny, neurons connecting the spine & feet may be over 1 metre long.

Structure of Neurons Cell Body-contains nucleus & organelles & produce neurotransmitter chemicals. Group of cell bodies outside CNS called Ganglion Dendrites-carry impulses towards the centre of the neuron to the cell body Axon- carry impulses away from the centre of the neuron to the cell body

Structure of Neurons Neurotransmitter vesicles-at the end of axons, these swellings release chemicals that carry the impulse from 1 cell to another. Chemicals called neurotransmitters Schwann cells, located along neurons, make myelin sheath. Myelin sheath, fat rich membrane that insulates the electrical impulses (MS patients lack this)

Interneurons Short neurons found in CNS. Not enclosed in Myelin sheath They connect motor & sensory nerves

Movement of Impulses When a neuron receives a stimulus an electrical impulse travels along the dendrite & axon to the neurotransmitter swellings The movement of the electrical impulse along a neuron involves the movement of ions. When an neuron is Not carrying an impulse ions are pumped in & out of the axon. This results in the inside of the axon being –ive and the outside +ive Threshold, is the minimum stimulus needed to cause an impulse

Movement of Impulses Once the threshold is reached the axon changes its permeability to ions At the site of stimulation the inside of the axon becomes +ive & the outside –ive. This change in charge causes the next section of the axon to alter its permeability A chain reaction is set up & a movement of +ive charges runs along the inside of the Axon. Energy (ATP) is needed to cause these changes Diagram 34.6 pg 322

Synapses Neurons are not connected to each other, they are separated by a small gap, Synaptic cleft. Synapse is the region where 2 neurons come into close contact. Electrical impulses cannot cross a synapse, instead they stimulate the neurotransmitter swellings to release a chemical substance (neurotransmitters), which diffuse across the synaptic cleft

Synapse After the nerotransmitters diffuse across the synaptic cleft the combine with receptors on the postsynaptic neuron. This causes an impulse to be regenerated The neurotransmitter is then broken down by enzymes. The digested NTs are reabsorbed into the neurotransmitter swellings and recycled.

The CNS-The Brain The brain contains over 1200 million neurons The brain & spinal cord is protected by bone & 3 membranes called Meninges Meningitis is an inflammation of these Meninges caused by virus or bacteria Viral meningitis is less severe Bacterial meningitis can lead to death

Structure of the Brain Cerebrum Largest part of the brain Outer part called cerebral cortex controls voluntary movements Right controls left Left controls right Strokes

Structure of the Brain Cerebellum Medula Oblongata controls muscular coordination 2nd largest Medula Oblongata involuntary once the process has been learned Controls breathing, blood pressure, swallowing, coughing Connects the spinal cord with the rest of the brain

Structure of the Brain Hypothalamus Thalamus links with pituitary gland located below the thalamus regulates the internal environment Thalamus located below the cerebrum sorting centre

Spinal Cord Composed of nerve tissue, surrounded by vertebrae which protects it. Transmits impulses to & from the brain Is located in the neural canal of the vertebrate The neural canal is lined by the meninges & contains cerebrospinal fluid Dorsal root carries sensory neurons into the spinal cord & the ventral root carries motor neurons out Dorsal & ventral roots combine to form 31 pairs of spinal nerves

Reflex Action Is a quick, automatic response to a particular stimulus.