Text: Chapter 5 Human Biology Stage 3

Keywords Central nervous system (CNS) Cerebrospinal fluid (CSF) Meninges Neurons Cell body Dentrites Axon Synapse Myelin sheath Schwann cells Sensory neurons Motor neurons Interneurons Cerebrum Cortex Convolusions Sulci Fissures - Longitudinal fissure Lobes Frontal Parietal Temporal Occipital Cerebellum Medulla oblongata Cardiac centre Respiratory centre Vasomotor centre Spinal cord Ascending tracts Descending tracts

The Nervous System The nervous system is the control centre and communication network of the body The nervous system can be divided into 2 parts: The central nervous system (CNS) The peripheral nervous system (PNS) The CNS includes the brain and the spinal cord The PNS is divided into the: Autonomic nervous system Sympathetic nervous system Parasympathetic nervous system Somatic nervous system Skeletal muscle Both the CNS and the PNS are also involved in maintaining homeostasis in conjunction with the endocrine system

Structure of nerve cells Nerve cells are called neurons. They are the functional unit of the nervous system. Neurons have: A cell body that contains the nucleus Dendrites, short extensions on one side of the cell body An axon, a long extension on the other side of the cell body

Structure of nerve cells Most axons are covered in a white, fatty material called the myelin sheath The myelin sheath is made up of individual cells called Schwann cells An axon with its covering is called a nerve fibre There are myelinated fibres and unmyelinated fibres

The myelin sheath Functions of the myelin sheath: It acts as an insulator It protects the axon from damage It speeds up rate of impulses It helps with the repair of injured fibres

The synapse The axon of one neuron connects to the dendrites of the next neuron There is a space in between the axon of the first neuron and the dendrites of the next one This space is called the synapse A nerve impulse travels from the dendrites, through the cell body, the axon, across the synapse and into the dendrites of the next neuron

Types of neurons: function Neurons are classified according to their function Sensory neurons carry messages from the receptors to the CNS Motor neurons carry messages from the CNS to muscles and glands Interneurons are located in the CNS and are the link between sensory and motor neurons

Types of neurons: structure Neurons can also be classified according to their structure: Multipolar neurons have one axon and multiple dendrites extending from the cell body. They are the most common type Bipolar neurons have one axon and one dendrite, both branching at their ends. They occur in the eye, ear and nose Unipolar neurons have just one axon extension and the cell body is to one side of the axon

The CNS Most of the neurons in the CNS are interneurons They have many branches that are able to send or receive messages The CNS consists of: grey matter, made up of neurons with unmyelinated fibres (axons) white matter, composed of neurons with myelinated fibres (axons) The brain is the control centre of the body The spinal cord goes out from the brain and sends a network of nerve fibres to the rest of the body

Protection of the CNS The brain and spinal cord are very delicate and important parts of the body and are highly protected 3 structures that support and protect the CNS: Bone Meninges Cerebrospinal fluid (CSF)

Protection of the CNS The brain is protected by the cranium The spinal cord runs through an opening called the vertebral canal surrounded by bony vertebrae

Protection of the CNS Inside the bone covering, the brain and the spinal cord have 3 layers of connective tissue called the meninges They cover the entire CNS Outler layer: tough and fibrous, sticks close to the bone Middle layer: lose mesh Inner layer: delicate, contains blood vessels, close to surface of the brain and spinal cord

Protection of the CNS CSF occupies a space between the middle and inner layers of the meninges It circulates through cavities in the brain and spinal cord It is a clear, watery fluid containing glucose, protein, urea and salts It acts as a shock absorber It acts as transport, taking nutrients to the brain and spinal cord and carrying waste away

The brain The brain is divided into 3 main sections Cerebrum Cerebellum Brain stem The cerebrum carries out the higher order functions Example: language The cerebellum is concerned with fine motor co-ordination Example: balance The brain stem carries out the lower order functions Example: breathing & heart rate

The cerebrum The cerebrum is the largest section of the brain It consists of two layers of grey matter sandwiching a layer of white matter The outer layer is called the cerebral cortex The cerebral cortex is greatly folded to increase surface area Folding produces convolutions which are separated by shallow downfolds called sulci and deep folds called fissures Grey matterWhite matter Sulci Fissures

The cerebrum The deepest fissure is the longitudinal fissure which separates the cerebrum into 2 halves; the left and right hemispheres Each cerebral hemisphere is divided into 4 lobes: the frontal, temporal, occipital and parietal lobes. Longitudinal fissure Cerebrum Cerebellum Spinal cord

The lobes Frontal lobe The boss – reasoning, planning Parietal lobe Sensory information – dealing with & reacting to the environment Occipital lobe Vision Temporal lobe Language, hearing, memory

The functional areas 3 functional areas in the cortex: Sensory area interprets impulses from receptors Motor area controls muscular movements Association areas concerned with emotional and intellectual processes – deciding how to respond

The cerebellum The cerebellum lies under the rear of the cerebrum It controls: Posture Balance Fine motor coordination (muscle movement)

The hypothalamus The hypothalamus lies in the middle of the brain between the two hemispheres It is mostly concerned with homeostasis

The medulla oblongata The medulla oblongata lies within the brain stem and contains the: Cardiac centre - regulates the rate and force of the heart beat Respiratory centre – controls the depth and rate of breathing Vasomotor centre - controls the diameter of blood vessels

The brain tch?v=kMKc8nfPATI The brain 13 mins

The spinal cord The spinal cord is a continuation of the brain stem It consists of gray matter in the shape of an H called the central canal which runs the length of the spinal cord and contains CSF

The spinal cord 3 functions of the spinal cord: It carries sensory impulses towards the brain It carries motor impulses away from the brain Reflexes – impulses that bypass the brain Myelinated nerve fibres of white matter are arranged in bundles called ascending and descending tracts Ascending tracts are sensory axons that carry impulses upwards towards the brain Descending tracts contain motor axons that conduct nerve impulses downwards away from the brain