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ANATOMICAL TERMS Anatomical stance Is a stance in which a person stand erect with the feet flat on the floor and close together, arms at their sides and the palms and face directed forwards? Body Planes o o o o o Sagittal Plane – Passes vertically though the body or an organ and it divides it into right and left positions Midsagittal (median) plane – The sagittal plane that divides the body or organ into equal halves Parasagittal Planes – Sagittal planes that are parallel to the medium and divide into unequal right and left portions Frontal (coronal) planes - Extends vertically but is perpendicular to the sagittal plane and divides the body into anterior and posterior positions Horizontal (cross-sectional or transverse) planes - Passed across the body or an organ perpendicular to its long axis; it divides the body or organ into superior (upper) and inferior(lower) portions Direction o o Plane – Frontal (Coronal) Anterior (ventral) – towards the front or belly Posterior (dorsal) – Towards the back or spine Plane – (Horizontal (Transverse) Superior (cranial) – Above o o o o o Inferior (caudal) – Below Plane – (Sagittal) Medial – Towards the median plane Lateral – Away from the medial plane Superficial – Closer to the body surface Deep – further from the body surface Proximal – Closer to the point of attachment of origin Distal – Further from the point of attachment of origin Movements o o o o o o o o o o o o o Flexion – Movement that usually decreases a joint angle, usually in the sagittal plane Eg: Bending elbow or knee Extension – Movement that straightens a joint and generally returns a body point to the zero position Eg: Straightening the elbow or knee Hyperextension – further extension of the joint passed through the zero position Eg: Whiplash Abduction – the movement of a body part in the frontal plane away from the midline of the body Eg: Moving feet apart to stand spread legged or raising one arm to one side of the body Adduction – movement in the frontal plane back towards the midline of the body Eg: Closing arms back to the chest Rotation – Movement in which a bone spins on its longitudinal axis Pronation – Movement causing the palm to face posteriorly or downwards Supination – Movement that turns the palm to face anteriorly or upwards Circumduction - One end of an appendage remains stationary while the other end makes a circular motion Eg: A baseball player throwing a ball Elevation – Movement that raises a body part vertically in the frontal plane Eg: Raising your eyebrows Depression – Lowers a body part in the same plane Eg: Lowering your eyebrows Inversion – Foot movement that tips the soles medially, somewhat facing each other Eversion – movement that tips the soles laterally away from each other NERVOUS SYSTEM Overview Central Nervous System – consists of the brain and the spinal cord, which are enclosed and protected by the cranium and vertebral column Peripheral Nervous System – consists of all the rest (somatic and motor), it is composed of nerves and ganglia o Nerves – a bundle of nerve fibres (axons) wrapped in fibrous connective tissue (CT) o Ganglia – a knot like swelling in a nerve where the cell bodies of neurons are concentrated o o Sensory (afferent) division – carriers signals from various receptors to the CNS Somatic sensory division – carriers signals from receptors in the skin, muscles, bone and joints Visceral sensory division – carriers signals mainly from the viscera of the thoracic and abdominal cavities Motor (efferent) division – carriers signals from the CNS to gland and muscle cells that carry out the body’s responses Somatic motor division – carriers signals to the skeletal muscles Visceral motor division (autonomic nervous system) – carriers signals to glands, cardiac muscles and smooth muscles Sympathetic division – tends to arouse body for action, accelerating the heartbeat Parasympathetic division – tends to have a calming effect, slowing the heartbeat a) Describe the embryological development of the nervous system. Embryonic Development The nervous systems develops from the ectoderm Within the first 3 weeks the neural plate forms along the midline of the embryo and sinks into the tissue to form the neural groove, with raised neural folds The neural folds’ roll towards each other and fuse By day 26 the neural folds form the neural tube As the neural tube develops it forms a neural crest Neural crest cells give rise to the peripheral nervous system, including the sensory and automatic nerves By the fourth week the neural tube forms the forebrain, midbrain and hindbrain Neural tube o Everything on the dorsal side is sensory o Everything on the ventral side is motor o Failure of the neural tube to close results in spina bifida o Somites are regular repeating pattern along the tube Each segment has a spinal nerve The spinal nerve is protected by vertebrae’s o Shingles is a viral infection that affects neurons Embryological Development Failure Spina Bifida o Indicates a failure of the dorsal portions of the vertebrae to fuse with each other o More severe forms, involve failure to close of more than one or two vertebrae, resulting in the meninges bulging through (meningocele) the opening or the meninges, spinal cord and nerves bulging out (meningomyelocele) o The more sever forms involve gradation of neurological symptoms which may include paralysis, loss of bladder and anal control and absence of reflexes o To prevent this condition females should have a high level of folic acid, when trying to have a child Anencephaly o Results from failure of the cephalic part of the neural tubes to close o The fore and mid brain do not develop fully o The cranial vault is also absent, resulting in the infant not surviving past birth Hydrocephaly o The circulation or drainage of CSF is obstructed resulting in a build-up in pressure o This result in abnormal skull in infants, as there skull is not yet fused, which can lead to possible retardation o This can be treated before birth by inserting a shunt which drains the fluid from the ventricles into a vein in the neck o In adults the skull is unable to grow and the brain is compressed causing pain, coma and then death if not treated b) Describe and identify gross anatomical features of the nervous system. Structure of a Neuron The control centre of a neuron is the soma/neurosoma/cell body o The soma usually gives rise to the dendrites, long, thin like branches They are the primary site for receiving signals from other neurons The more dendrite a neuron has the more information it can receive 5 to 135 micro metres in diameter o Axon - a cylindrical and relatively unbranched for most of its length Specialised for rapid conduction of nerve signals to points remote from the soma 1 to 20 micro metres long Neuron Classifications o Multipolar Neurons – one axon and multiple dendrites o Bipolar Neurons – one axon and one dendrite o Anaxonic Neurons – multiple dendrites and no axons Axonal Transport Axonal transport – the two-way passage of proteins, organelles and other materials along an axon Anterograde transport – movement away from the soma down the axon Retrograde transport – movement up the axon toward the soma Fast axonal transport – occurs at a rate of 20 to 400 mm/day and may either be anterograde or retrograde o Fast anterograde transport – moves mitochondria, synaptic vesicles o Fast retrograde transport – returns used synaptic vesicles and other material to the soma and informs the soma of the conditions of the axon terminals Slow axonal transport – an anterograde process that works in a stop and go fashion, moves at 0.5 to 10 mm/day o Moves enzymes and cytoskeletal components down the axon Types of Neuroglia Neuroglia of CNS o Oligodendrocytes – form myelin in brain and spinal cord o Ependymal cells – line cavities of brain and spinal cord o Microglia – destroys microorganisms, foreign matter and dead nervous tissue o Astrocytes – cover brain surface Neuroglia of PNS o Schwann cells – forms a myelin sheath around nerve in the PNS o Satellite cells – surround somas of neurons in the ganglia Myelin Myelin sheath is a spiral layer of insulation around a nerve fibre, formed by oligodendrocytes in the CNS and Schwann cells in the PNS Production of the myelin sheath is called myelination, begins at the 14th week of foetal development Conduction speed of Nerve Fibres The speed at which a nerve signal travels along a nerve fibre depends on two facts, the diameter of the fibre and the presence or absence of myelin o Travel fast in the presence of myelin Local Potentials Stimulation of neuron causes local disturbances in membrane potential Depolarization – any such case in which the voltage shifts to a less negative value Local Potential – Short range change in voltage Characteristics o Graded – they vary in magnitude (voltage) per the strength of the stimuli An intense or prolonged stimulus opens more ion channels than a weaker stimulus o Decremental – they get weaker as they spread from the point of stimulation o Reversible – if stimulation ceases, cation diffusion out of the cell quickly returns the membrane voltage to its resting potential o Either excitatory or inhibitory Action Potentials Action potential – a more dramatic change produced by voltage-gated ion channels in the plasma membrane Characteristics o All or non-law – the neuron will only fire if the threshold has been reached o Non-decremental – they do not get weaker with distance o Irreversible – if a neuron reaches threshold, the action potential goes to completion, it cannot be stopped once it begins Threshold – the minimum needed to open voltage-gated channels Refractory period – during an action potential and for a few milliseconds after, it is difficult or impossible to stimulate that region of a neuron to fire again o Absolute refractory period – no stimulus of any strength will trigger a new action potential o Relative refractory period – it is possible to trigger a new action potential, but only with an unusually strong stimulus Local vs Action Potential Local Potential Produced by gated channels of the dendrites and Soma May be positive (depolarizing) or negative (hyperpolarizing) voltage change Graded; proportion to stimulus strength Reversible Local Decremental Action Potential Produced by voltage-gated channels on the trigger zone and axon Always begins with depolarization All or none Irreversible Self-propagating Nondecremental Spinal Cord – Structure A cylinder of nervous tissue that arises from the brainstem at the foramen magnum of the skull 45cm long and 1.8cm thick During embryological development, the spinal cord extends for the full length of the vertebrae, but since the vertebrae grows faster than the spinal cord, the cord only extends to L3 by the time of birth and to L1 in an adult 31 pairs of spinal nerves o The part supplied by each pair of nerves is called a segment Region of Spinal Cord Cervical Thoracic Lumbar Sacral Coccygeal Number of pairs of nerves 8 12 5 5 1 Spinal cord is divided into cervical, thoracic lumbar and sacral regions Thicker in two areas o In the inferior cervical region, a cervical enlargement gives rise to nerves of the upper limbs o In the lumbosacral region, lumbar enlargement that issues nerves to the pelvic region and lower limbs Cauda equine is a bundle of nerve roots Spinal cord is enclosed by three fibrous membranes called meninges, that separate the soft tissue of the central nervous system from the bones of the vertebrae and skull o Dura mater – forms a loose-fitting sleeve called the Dural sheath around the spinal cord Tough, collagenous membrane Epidural space – space between the sheath and vertebral bones, that is occupied by blood vessels, adipose tissue and loose connective tissue Epidural anaesthesia – anaesthetics introduced to this space to block pain signals during childbirth or surgery o Arachnoid mater – a loose mesh of collagenous and elastic fibers spanning the gap between the arachnoid membrane and the pia mater Simple squamous epithelium Subarachnoid space – gap between the arachnoid membrane and the pia mater that is filled with cerebrospinal fluid o Pia mater Delicate, transparent membrane that closely follows the contours of the spinal cord Cross sectional anatomy o Consists of two kinds of nervous tissue called grey and white matter Grey matter – relatively dull colour because it contains little myelin White matter – bright, pearly white appearance due to an abundance of myelin There is more white matter on sections of the spinal cord that are closer to the brain since there are more ascending and descending tracts closer to the brain o Axons run through white matter Surrounds the grey matter Spinal tracts o Ascending tracts – carry sensory information up the cord Example Gracile fasciculus – carries signals from the mid thoracic and lower parts of the body Cuneate fasciculus – joins the gracile fasciculus at the T6 level Spinothalamic tract – carriers signals for pain, temperature, pressure, tickle, itch and touch Spinoreticular tract – carries pain signals resulting from tissue injury Posterior and anterior spinocerebellar tracts – carry proprioceptive signals from the limbs and trunk to the cerebellum at the rear of the brain o Descending tracts – conduct motor impulses down Example Corticospinal tract – carry motor signals Tectospinal tract – involved in reflex turning of the head Lateral and medial reticulospinal tract – control muscle of the upper and lower limbs Lateral and medial vestibulospinal tract – control of extensor muscles of the brain o Decussation – the tracts cross over from the left side of the body to the right As a result the left side of the brain receives sensory information from the right side of the body and sends motor commands to that side Neurons Neurons are cells 10^10 neurons Predominantly the same structure A living cell with a nucleus Neurons cannot divide The Brain Rostral – towards the forehead Caudal – towards the spinal cord Three major portions of the brain (Major parts of CNS) o Cerebrum 83% of brains volume Grey matter on outside Marked by thick folds called gyri and separated by shallow grooves called sulci The longitudinal fissure separates the right and left portion The hemispheres are connected by a thick bundle of nerve fibers called the corpus callosum