Nervous System

• The nervous system is a complex network of nerves and cells that carry messages to and from the brain and spinal cord to various parts of the body • Contains the Central Nervous System and the Peripheral Nervous System

• The Brain and Spinal cord needs to be protected as they are vital parts of the body • There are structures that protect the CNS, they include; bone, membranes called meninges, cerebrospinal fluid (CSF)

• Outermost part is the protective layer • Cranium protects brain • Vertebral canal protects the spinal cord

• Meninges are membranes formed by 3 layers of connective tissue, they cover the entire CNS • Outer Layer, tough and fibrous, sticks close to the bones of the skull but not so close to the vertebral canal • Middle Layer, contains loose mesh fibres • Inner Layer, more delicate, contains blood vessels, sticks closely to the surface of the brain and spinal cord

• Formed from the blood and it circulates around and through the CNS, eventually re-entering the blood capillaries • Occupies the space between the middle and inner layers of meninges, it also circulate through cavities in the brain and through a canal in the centre of the spinal cord • It is a clear watery fluid, which contains some cells, glucose, proteins, urea and salts • Protection: Acts as a shock absorber, cushioning any blows or shocks the CNS may sustain • Supports: The brain is suspended inside the cranium and floats in the fluid that surrounds it • Transport: Takes nutrients to the cells of the brain and spinal cord and carries away their wastes

• Cerebrum: largest part of the brain, surface is folded into convolutions • Corpus Callosum: a large bundle of nerve that connects the left and right hemispheres • Cerebellum: underneath the rear end of the brain, the folds are less prominent than those of the cerebrum • Medulla Oblongata: joins the brain and spinal cord • Hypothalamus: deep inside the brain, responsible for many important functions such as water balance and temperature

• Biggest part of the brain, involved in mental activities such as thinking, learning, memory, perception and control of voluntary muscle contraction • Consists of an outer surface of grey matter known as the cerebral cortex • Below the cortex is white matter and deep inside the cerebrum is additional grey matter called the Basal Ganglia • The Cerebral Cortex is folded into patterns which greatly increase the surface area, these are called convolutions GYRI • The convolutions are separated by SUCLi (shallow down folds) or fissures (deep down folds) • Right and Left Cerebral Hemispheres are subdivided into 4 lobes: frontal, parietal, temporal and occipital

~Sensory areas- receive and process nerve impulses from the sense ~Motor areas - send impulses to muscles especially for voluntary movement ~Association areas - Interpret information form the sense and make it useful

• Lies under the rear part of the cerebellum • It is the second largest part of the brain and its surface is folded into a series of parallel ridges • The outer folded part of the Cerebellum is grey matter (unmyelinated nerve fibre) and inside contains white matter (myelinated fibres) that branches to all parts of the cerebellum • The Cerebellum exercises control over posture, balance and the fine coordination of voluntary muscle movement • Functions that occur are unconscious • Without the cerebellum our movements would be jerky and uncontrolled

• The Medulla Oblongata is a continuum of the Spinal Cord, about 3cm long • Many nerve fibres pass through the medulla going to or from other parts of the brain • The Medulla Oblongata plays an important role in automatically adjusting body functions, it contains; ~The Cardiac Centre, which regulates the rate and force of heartbeat ~Respiratory Centre, which control rate and depth of breathing ~Vasomotor Centre, which regulates the diameter of the blood vessels • There are also centres that regulate the reflexes of swallowing , sneezing and vomiting, all centres in the medulla oblongata are influenced and controlled by higher centres in the brain, particularly the hypothalamus

• The spinal cord extends from the foramen magnum, the large opening at the base of the skull to the second lumbar vertebrae, which is at about waist level • About 44cm in length • Function is to carry sensory impulses to the brain and motor impulses down from the brain • The second functions is to integrate certain reflexes • Contains grey matter in the centre, in the shape of a letter H • The myelinated nerve fibres of white matter are arranged in bundles known as ascending and descending tracts • Ascending tracts are sensory axons that carry impulses upwards towards the brain • Descending tracts contain motor neurons that conduct impulses downwards away from the brain

• Contains nerve fibres • Carries info to and from CNS and to groups of nerve cell bodies (ganglia) which lie outside brain & spinal cord • Contains autonomic (which contain two sub divisions; sympathetic and parasympathetic) and somatic nervous systems

• Carries messages to skeletal muscles and involved in voluntary muscle movements • Takes impulses from the CNS to the skeletal muscles

• Apart of the Peripheral Nervous System • Operates without conscious control and is regulated by groups of nerve cells in the Medulla Oblongata, Hypothalamus and Cerebral Cortex • Body functions regulated by the autonomic nervous system include; heart rate, blood pressure, body temperature, digestion, release of energy, pupil diameter, airflow to lungs, defecation and urination • Carry messages to heart muscle and other internal organs and the glands

• Apart of the Peripheral Autonomic Nervous System • “Rest and Digest” • Enables maintenance of normal bodily functions such as digesting and keeping the body at rest e. g. constriction of pupils, stimulation of saliva, stimulation of stomach activity

• Apart of the Peripheral Autonomic Nervous System • Produces responses that prepare the body for strenuous physical activity • Function is to stimulate the ‘fight or flight’ response which is a physiological reaction that happens in response to a perceived harmful event, attack or threat to survival e. g. dilation of pupils, increased heartbeat, dilation of airways and increase depth of breathing

The basic structural and functional units if the whole nervous system the three main components of a neuron are: dendrites, cell body & axon

Many branches that receive messages from the other neurons and carry them towards the cell body

• Only one, often is long and unbranched for most of its length • Axons carry impulses away from the cell body, most axons are covered with a layer of fatty material called the myelin sheath

• Layer of fatty material formed by Schwann cells which wrap around axons • Those that have myelin sheath are known as myelinated fibres and those which do not are said to be unmyelinated fibres • Myelin Sheath have three important function; to act as an insulator, protect the axon from damage and to speed up movement of nerve impulses along the axon

• Grey matter consists of nerve cell bodies and unmyelinated fibres • White matter consists of nerve cells bodies composed of myelinated fibres

The outermost part of the Schwann cell which helps repair injured fibres

• Sensory Neurons - carry messages from receptors in the sense organs, or in the skin, to the Central Nervous System • Motor Neurons - carry messages from the central nervous system to the muscles and glands (the effectors) • Interneuron Neurons - located on the central nervous system and are the link between the sensory and motor neurons

• Multipolar - most common, 1 Axon and multiple dendrites extending from the cell body, interneurons and motor neurons • Bipolar - 1 axon and 1 dendrite, axon and dendrites may have branches on the ends, take impulses from the receptor cells (sensory neuron) to other neurons • Unipolar - 1 axon, cell body is to one side of the axon are most sensory neurons that carry messages to the spinal cord