The Nervous System

The Nervous System

The Nervous System The nervous system is divided up into two regions: The central nervous system (CNS) – brain and spinal cord The peripheral nervous system (PNS) – vast network nerves

What is a stimulus? A stimulus is any change in the environment that may cause a response.

Processes that are involved to a response to a stimulus: Reception: stimulus must be detected by neurons (nerve cells) and sense organs. Transmission: message is carried along the neurons (PNS carry messages to and from the CNS). Integration: messages are sorted and processed by the CNS (brain) Response: carried to the effectors (muscles and glands)

Diagrams of the nervous system

Neurons A neuron is a nerve cell Three types of neurons: Sensory neuron (afferent) Motor neuron (efferent) Interneurons

Sensory neuron Takes messages from sense organ to the CNS

Motor neuron Take messages from the CNS to muscles and glands causing them to respond.

Comparing sensory and motor neurons

Interneuron Carries information between the sensory and motor neurons. Only found in the CNS.

Parts of a neuron: Receptors: cells that detect a stimulus Nerve endings: connect sensory neurons to receptor cells or sense organ. Dendrites: fibres that carry impulses towards the cell body Axons: carry impulses away from the cell body Schwann cells: they make the myelin sheath

Parts of the neuron: Myelin sheath: fat rich membrane that insulates the eletrical impulses. NOTE: Multiple sclerosis (MS) patches of the myelin sheath degenerates and slows down the nerve impulses causing numbness and paralysis to loss of bladder control. Cell body: contains the nucleus, forms the dendrites and axons NOTE: a group of cell bodies located outside the CNS is called a ganglion. NOTE: Cell bodies in sensory neurons are located outside the CNS, cell bodies of motor neurons are located within the CNS.

Parts of the neuron: Neurotransmitter swellings: release chemicals that carry the impulses from one nerve cell to another. NOTE: these chemicals are called neurotransmitters Motor neuron

Interneurons Short neurons Found in the CNS Connect the motor neuron to the sensory neuron.

Synapse A synapse is a region where two neurons come into close contact (between axon terminals and dendrites of two neurons) Synaptic cleft: is a tiny gap between the two neurons at a synapse.

Synapse The gap in the synaptic cleft is 0.00002 mm. One neuron can have 10000 synapses in the brain.

Activation of neurotransmitter Electrical impulses cannot cross a synapse. The message is carried by chemicals that are released by the neurotransmitter swellings in the presynaptic neuron (they diffuse across synaptic cleft) NOTE: these chemicals are known as neurotransmitters.

Activation of neurotransmitter Neurotransmitters are contained in vesicles in the neurotransmitter swellings. Neurotransmitters diffuse across the synaptic cleft which cause the electrical impulses to be regenerated in the postsynaptic cleft.

Inactivation of neurotransmitter Neurotransmitters (chemicals) are then broken down by enzymes. They are digested and reabsorbed back into the neurotransmitter swellings. Electrical Chemical Electrical Impulse impulse impulse Examples of neurotransmitters: acetylcholine (Ach) and nodadrenalin

Structure of a synpase

Functions of synapse: Transmit impulses from one neuron to another neuron They control the direction of the impulse and only allow it to pass in one direction (neurotransmitter swellings are only found on the presynaptic side of synapse) Impulse can be blocked by certain chemicals (painkillers) Prevent overstimulation of effectors (muscles or glands) -- neurotransmitters stop being produced due to constant stimulation such as pain or noise. Neuronal Synaptic Cleft - A Level Biology - YouTube

Nervous System disorder Cause: It is caused by the failure to produce a neurotransmitter called dopamine in part of the brain. Lack of dopamine results in the ability to control muscle contraction. Causes trembling in hands and legs (eating and washing become difficult). Mainly occurs in the elderly and males

Parkinson’s disease

Parkinson’s disease Prevention: No known treatment for Parkinson’s disease Treatment: Physiotherapy and special exercises Drugs that stimulate dopamine (reduce symptoms) Michael J Fox Parkinson's Disease – YouTube Treating Parkinson's Disease with Deep Brain Stimulation - YouTube Deep Brain Stimulation (DBS) Parkinsons Australia – YouTube Walking Before/After DBS for Parkinson's Treatment – YouTube Neurotransmitters animation - YouTube

Spinal cord Composed of nerve tissue Surrounded by vertebrae which protect it.

Spinal cord Located in the neural canal of vertebrae and is lined with the meninges. Dorsal root carries sensory neurons into the spinal cord. Ventral root carries motor neurons out of spinal cord. They are linked by inter neurons in the grey matter. Dorsal root swellings contain ganglia (groups of cell bodies of sensory neuron)

Spinal cord In the centre of the grey matter in the central canal, contains the cerebrospinal fluid.

Peripheral Nervous System Consists of nerves away from spinal cord Cell bodies of sensory neurons are located in the ganglia in the PNS (in dorsal root) Cell bodies of motor neurons are located in the CNS (grey matter)

Reflex action A reflex action is an automatic, involuntary, unthinking response to a stimulus. The nerve impulses that are carried by the neurons make up the reflex arc. The spinal cord controls many reflex actions.

Examples of reflex actions: Movement of iris in the eye Blinking of eyes for protection Breathing Control of blood pressure

Advantages of reflex actions: Allow for fast responses to protect the body from damage (pulling hand away from hot flame)

Withdrawal action Receptors in the fingers are stimulated by a hot flame. Sensory neurons carry impulses into the spinal cord. An interneuron carries the impulse across the spinal cord to a motor neuron. Another neuron takes the impulse up to the brain. Motor neuron takes impulse straight out of spine to effector (muscle or gland) which causes us to pull our hand back from hot flame. At the same time as the hand is withdrawn, the impulse reaches the brain which makes us aware of what has happened and we feel some pain.