Anatomy Notes Week 12 PDF

Peripheral Nervous System (PNS) 1. Cranial nerves – 12 pairs cerebrum midbrain pons medulla oblongata sensory, motor, name or both mnemonic I – olfactory odour some II – optic observation say III – oculomotor orbit marry IV – trochlear to money V – trigeminal touch but VI – abduc...

Peripheral Nervous System (PNS) 1. Cranial nerves – 12 pairs cerebrum midbrain pons medulla oblongata sensory, motor, name or both mnemonic I – olfactory odour some II – optic observation say III – oculomotor orbit marry IV – trochlear to money V – trigeminal touch but VI – abducens and my VII – facial face brother VIII – vestibulocochlear v(ear)y says* IX – glossopharyngeal gustatory big X – vagus voice brains XI – accessory and matter XII – hypoglossal holler more Peripheral Nervous System 2. Spinal nerves – 31 pairs; all are ‘mixed’ nerves (contain both sensory and motor neurons) cervical i) 8 cervical (C1– C8) ii) 12 thoracic (T1– T12) thoracic iii) 5 lumbar (L1– L5) iv) 5 sacral (S1– S5) v) 1 coccygeal (Co1)  all exit the spine via intervertebral foramina, except for C1 (exits between the atlas and occipital) lumbar sacral coccygeal 2) Spinal nerves Nerve connective tissue: a) epineurium  surround axon endoneurium the whole nerve perineurium b) perineurium  around groups of fibres (=fascicle) epineurium c) endoneurium  around each individual (axon + myelin) fibre fascicle 2) Spinal nerves Each spinal nerve has two points of attachment to the spinal cord: a) dorsal root – contains axons of sensory neurons  cell bodies located in dorsal root ganglia (swellings of gray matter) dorsal root dorsal root ganglion spinal nerve lateral horn ventral horn ventral root b) ventral root – contains axons of autonomic and somatic motor neurons  cell bodies located in ventral or lateral horns 2) Spinal nerves Spinal nerve: joining of the dorsal and ventral roots Spinal nerves are short and quickly branch, forming rami: i) dorsal ramus  innervate the ii) ventral ramus dorsal ramus ventral ramus spinal nerve skin and muscles of the back rami communicantes sympathetic trunk ganglion  become thoracic nerves T2– T12, or join together with other ventral rami to form nerve plexuses iii) rami communicantes – carry autonomic nerve fibres from the ventral rami to sympathetic trunk (paravertebral) ganglia  forms a pathway that connects preganglionic and postganglionic neurons of the sympathetic nervous system Spinal nerve plexuses (interlacing nerve networks) Formed from the joining of ventral rami of several nerves Formed by spinal nerves: Major nerves arising from: i) cervical C1 – C5 phrenic (innervates diaphragm) ii) brachial C5 – C8; T1 axillary, radial, ulnar, median, musculocutaneous (shoulder, upper limbs) iii) lumbar L1 – L4 femoral (hip, lower limbs) iv) sacral L4 – S4 sciatic; divides into tibial and common fibular (posterior thigh and calf) Plexus Nervous System Sensory (Afferent) Systems – monitor changes in environment stimulus receptor CNS Classified by: a) location i) exteroceptors – detect stimuli from outside the body  located at or near the body surface e.g. touch, pain, pressure, and temperature receptors; most ‘special senses’ (vision, hearing, smell, taste) heat/ cold touch pain pressure a) location ii) interoceptors – detect internal stimuli  in viscera, blood vessels baroreceptor e.g. chemical, pressure, and (internal) temperature receptors iii) proprioceptors – detect internal stimuli (stretch)  in skeletal muscle, joints, and associated connective tissue  monitor muscle activity, position of joints, and body orientation Sensory Systems: classification b) type of stimulus i) mechanoreceptors – mechanical stimuli e.g. pressure, touch, stretch, vibration (hearing) ii) thermoreceptors – temperature iii) chemoreceptors – chemical signals e.g. taste, smell, blood chemistry iv) photoreceptors – sense light v) nociceptors – pain e.g. extreme heat, cold, pressure; can be external or internal Sensory Systems: classification c) structure – applies only to the ‘general senses’ i) free nerve endings  terminal dendrites of unipolar sensory neurons e.g. pain, itch, root hair plexus ii) encapsulated  terminal dendrites enclosed in connective tissue e.g. Meissner’s and Pacinian corpuscles Neuronal Pathways Ascending (sensory) pathways – afferent  conduct impulses from general sense receptors to the brain Spinal pathways – most are a chain of three successive neurons: a) 1st order neurons – unipolar; from receptor to the CNS  cell body located in PNS; sensory ganglia of cranial nerves 1st order or dorsal root ganglia of spinal nerves neuron  axon terminates in the dorsal horn of the spinal cord or the medulla dorsal root ganglion dorsal horn Spinal pathways b) 2nd order neurons – multipolar interneurons 3rd order neuron  cell body in the dorsal horn of the spinal cord or the medulla thalamus cerebrum  most decussate in the medulla or the spinal cord  transmit impulses to the thalamus (or the cerebellum cerebellum where the tract terminates) 2nd order neuron c) 3rd order neurons – multipolar interneurons  cell body medulla in the thalamus  transmit impulses to the somatosensory cortex (postcentral gyrus of cerebrum) cervical 1st order neurons lumbar Spinal pathways Ascending tracts of the spinal pathways a) posterior (dorsal) column pathways  receptors = free nerve endings, Meissner’s, etc.  tracts for the direct transmission of signal from receptor to the sensory cortex – ‘specific’ pathway cerebrum  thus, sensations (e.g. touch) can be precisely discriminated/located on the body b) spinocerebellar pathways  receptors = cerebellum medulla proprioceptors  ascending tract from spinal cord to cerebellum cervical  no 3rd order neurons; no decussation; no conscious perception of stimulus (e.g. balance) lumbar Ascending tract pathways c) anterolateral (spinothalamic) pathways  receptors = temperature, pain cerebrum  2nd order neurons decussate in the spinal cord  carry signals from multiple types of receptors to the thalamus they synapse with multiple 3rd order neurons, thus forming ‘non-specific’ pathways  here  i.e. you are aware of the stimulus but it is difficult to precisely localize where it originated from cerebellum medulla cervical lumbar Nervous System Motor Systems – efferent; always multipolar neurons CNS effector(s) cerebrum 1. Somatic NS – effector = skeletal muscle midbrain a) upper motor neurons – CNS interneurons  form descending tracts of motor pathways cerebellum i) direct motor (pyramidal) pathways  cell bodies  no  for located in the cerebral motor cortex synapses within the brain  axons medulla cervical of most tracts decussate in the medulla precise voluntary movements lumbar 1. Somatic Nervous System ii) indirect motor pathways – complex, multi-synaptic tracts cerebrum  cell bodies in midbrain receive/integrate impulses from motor cortex, basal nuclei, and cerebellum  descending tracts immediately decussate  important for balance, muscle tone, coarse movements, and following moving objects by the head, neck, and eyes midbrain cerebellum b) lower motor neurons – true motor neurons medulla  cell bodies in ventral horn of spinal cord (CNS)  exit the spinal cord and directly innervate the skeletal muscles (axons are in the PNS) cervical Upper and lower motor neurons often separated by interneurons Motor Systems 2. Autonomic NS (ANS)  multipolar neurons  effectors = cardiac muscle, smooth muscle, glands Two neuron pathway: a) preganglionic neuron – lightly myelinated  cell bodies in the brainstem or lateral horn of the spinal cord b) postganglionic neuron – unmyelinated  cell bodies CNS in autonomic ganglia (outside of the CNS) PNS Preganglionic (myelinated) autonomic ganglion Postganglionic (unmyelinated) EFFECTOR 2. Autonomic Nervous System Subdivisions of ANS: a) sympathetic NS  excitatory* b) parasympathetic NS  inhibitory* 2. Autonomic Nervous System Comparison of SNS and PSNS SNS PSNS i) cell body of preganglionic neuron lateral horns of T1–L2 ii) autonomic ganglia close to spinal cord; terminal ganglia lateral (in trunk) or in or near visceral collateral (anterior) effector organs iii) postganglionic neuron long axons short axons iv) function fight or flight rest and digest v) nerves exit CNS mainly as thoracic nerves mainly (80%) via the vagus nerve brainstem, S2–S4 Special senses A. Eye a three-layered sphere filled with fluid sclera 1. Fibrous tunic – superficial layer a) sclera (white) – tough, avascular CT cornea  surrounds the anterior margins and posterior region of the eye b) conjunctiva – vascular mucus membrane  covers the anterior sclera  ‘bloodshot eyes’ when blood vessels become dilated c) cornea (transparent) – avascular CT  circular, anterior ‘window’ for light to enter the eye A. Eye 2. Vascular tunic a) choroid (posterior eye) – highly vascular  contains melanin choroid ciliary body b) ciliary body – anterior; encircle the lens i) ciliary muscles (smooth muscle) control lens shape and cause the lens to focus ii) ciliary processes secrete aqueous humor c) iris – pigmented part of the anterior eye iris pupil d) pupil – round central opening of each eye in the central iris A. Eye 3. Nervous (sensory) tunic – ‘retina’ a) outer pigmented layer – single layer of epithelial cells b) inner neuronal layer; contains: retina i) photoreceptors (superficial)  rods – dim light vision; black and white  cones – high resolution; colour perception light ii) bipolar cells rods  transmits rod and cone signals to... iii) ganglion cells (deep)  axons form optic nerve (II) ganglion cells bipolar cells pigmented epithelium cones A. Eye 3. Nervous (sensory) tunic – ‘retina’ c) fovea centralis – no rods, just cones fovea centralis  where light is focused; forms the area of greatest visual acuity optic disk d) optic disk – ‘blind spot’  no rods or cones  where the optic nerve and blood light rods vessels exit the eye ganglion cells bipolar cells pigmented epithelium cones A. Eye 4. Lens – biconvex and flexible; focuses light  avascular; transparent  cataracts – clouding of lens 5. Anterior segment – anterior to the lens lens aqueous humor  contains a fluid similar in composition to plasma termed the aqueous humor  replaced every ~90 min 6. Posterior segment – posterior to the lens  contains a gel-like vitreous humor  permanent; not replaced vitreous humor Special senses auricle B. Ear 1. External ear – directs sound inward a) auricle – ‘pinna’  elastic cartilage covered with skin external auditory canal b) external auditory (acoustic) canal – ‘meatus’ c) tympanic membrane – ‘eardrum’  sound waves causes it to vibrate tympanic membrane B. Ear 2. Middle ear – an air-filled cavity a) ear ossicles – conducts sound to the inner ear i) malleus – ‘hammer’  attached to incus the eardrum malleus stapes ii) incus – ‘anvil’ iii) stapes – ‘stirrup’  attached to the oval window pharyngotympanic tube b) pharyngotympanic tube – ‘Eustachian tube’  links the middle ear with the nasopharynx; helps equalize middle ear pressure B. Ear 3. Inner ear – ‘labyrinth’; detects sound, important for equilibrium a) bony labyrinth  ‘tunnels’ in  are temporal bone fluid-filled (perilymph) i) semicircular canals semicircular canals (3)  equilibrium ii) vestibule  equilibrium iii) cochlea  hearing vestibule cochlea 3. Inner ear b) membranous labyrinth – suspended in perilymph  surrounded and protected by the bony labyrinth  contains endolymph fluid i) semicircular ducts (3)  inside the canals semicircular ducts ii) utricle and saccule  inside the vestibule iii) cochlear duct  inside the cochlea utricle saccule cochlear duct B. Ear Cochlea – coiled (‘snail shell’)  each coil has three separate channels a) scala vestibuli  upper; contains perilymph b) cochlear duct (scala media)  middle; contains endolymph c) scala tympani scala vestibuli cochlear duct  lower; contains perilymph scala tympani Cochlea Cochlear membranes: a) vestibular membrane  between the cochlear duct and the scala vestibuli b) basilar membrane  between the cochlear duct and the scala tympani c) tectorial membrane  covers tectorial membrane the hair cells basilar membrane vestibular membrane B. Ear 4. Inner ear receptors – mechanoreceptive hair cells with cilia (‘hairs’) that detect sound waves  the cilia tips extend into the endolymph of the cochlear duct and are embedded in the tectorial membrane (hold the cilia in place) tectorial membrane cilia When activated, hair cells send electrical impulses to the brain via cranial nerve VIII (vestibulocochlear nerve) hair cell