A&P Ch 12 & 13 Notes PDF

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Anatomy and Physiology Chapter 12 & 13 Lecture Notes (Spinal Cord Anatomy), Teacher: Dr. Olivey
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Chapters 12a and 13b ADULT SPINAL CORD: - divided into 4 regions (cervical, thoracic, lumbar, and sacral) - 31 segments ( determined by the origin of the spinal nerves; named for the vertebral location) - ends between L1 and L2 GROSS ANATOMY OF THE ADULT SPINAL CORD: - Localized enlargements provide interaction to limbs (cervical enlargement, lumbar enlargement) - Conus Medullaris: tapered conical portion of the spinal cord below lumbar enlargement - Filum Terminale: fibrous tissue that supports the spinal cord below the conus medullaris - Posterior Median Sulcus - Anterior Median Fissure - Central Canal SPINAL MENINGES: - Continuous with the 3 layers of the brain (Dura Mater, Arachnoid, Pia Mater) - Dura Mater: longitudinal collagen fibers - Arachnoid: elastin and collagen fibers, lined with simple squamous epithelium, subarachnoid space contains CSF

- Pia Mater: meshwork of elastin and collagen fibers, Denticulate Ligaments (extend from pia mater to dura mater)

SECTIONAL ANATOMY OF THE SPINAL CORD: - White Matter: myelinated and unmyelinated axons; exterior portion of the spinal cord - Gray Matter: cell bodies, unmyelinated axons and neuroglia; interior portion of the spinal cord - Horns: projections of gray matter toward outer surface of cord - Nuclei: cluster of neuron cell bodies in the gray matter of the brain or spinal cord - Ganglia; cluster of neuron cell bodies outside the CNS HORNS OF SPINAL CORD: - Posterior Gray Horn: contains somatic and visceral sensory nuclei - Anterior Gray Horns: deal with somatic motor control - Lateral Gray Horns: contain visceral motor neurons - Gray Commissures: contain axons that cross from one side to the other WHITE MATTER: - Divided into columns (funiculi) containing tracts - Ascending Tracts: relay information from the spinal cord to the brain (sensory tracts) - Descending Tracts: carry information from the brain to the spinal cord (motor tracts)

ORGANIZATION OF SPINAL CORD GRAY MATTER: - Mixed Nerves - Each set of nerves are paired (left and right) with dorsal roots and ventral roots - Dorsal Roots: contain sensory axons, somas are in the dorsal root ganglion - Ventral Roots: contain axons of motor neurons ORGANIZATION OF SPINAL NERVES:

SPINAL NERVES: - Mixed Nerves: contains both sensory and motor neurons; each set of nerves are paired (left and right) with dorsal roots and ventral roots - Dorsal Roots: contain sensory axons, somas are in the dorsal root ganglion - Ventral Roots: contains axons of motor neurons NERVE PLEXUS: - Complex interwoven network of nerves from different spinal nerves made of mixed nerves (contain both sensory and motor neurons); only form from ventral rami FOUR LARGE PLEXUSES:

- Cervical Plexus: innervates neck, thoracic cavity, diaphragm, phrenic nerve - Brachial Plexus: innervates pectoral girdle and upper limbs - Lumbar and Sacral Plexus: innervate the pelvic girdle and lower limbs, sciatic nerve DERMATOMES OF THE BODY: - Dermatome: an area of skin innervated by branches of a particular spinal nerve - Important for anesthesia, diagnosing SC injury - Some overlap, damage to a single neve won’t usually cause absolute numbness in trunk

Chapters 12 and 13 (parts) NEURAL ANATOMY 6 MAJOR REGIONS AND LANDMARKS: - Cerebrum: - gyri (us): ridges - sulci (us): grooves or fissures - Cerebellum: involved in motor control - Diencephalon: surrounded by the cerebrum - Thalamus: sensory integration - Hypothalamus: emotions, ANS, hormone control - Mesencephalon: (midbrain) auditory and visual processing - Pons: somatic and visceral motor control - Medulla Oblongata: autonomic control of breathing, heart rate, and blood pressure MEDULLA AND PONS: - Medulla Oblongata: similar to spinal cord, contains tracts going to and

from the other brain region, has centers that control heart rate, respiration, and blood pressure - Pons: mostly contains fiber running through it, has some centers that modulate the medulla MIDBRAIN: - Contains important reflux nuclei - Substantia Nigra: motor center, dopamine, parkinson disease - Superior Colliculus(us): visual reflexes - Inferior Colliculi(us): auditory reflexes - Red Nucleus: motor reflexes in lower animals (e.g. walking) - Corpora Quadrigemina = Superior Colliculi(us) and Inferior Colliculi(us) THALAMUS AND HYPOTHALAMUS: - Contains numerous nuclei - Thalamus: major relay station to the cerebral cortex, all sensory information stops here first (except smell), can act on it, ignore it or send it to cerebrum - Hypothalamus: link between endocrine and neural systems, controls strong emotions, autonomic./essential body functions, produces hormones ADH and oxytocin CEREBELLUM: - Cerebellar Peduncles: 3 sets of large tracts going to other brain regions (superior, inferior, lateral) BRAIN LOBES AND REGIONS: - Frontal Lobe: voluntary motor function, motivation, aggression, sense of smell, mood - Precentral Gyrus: primary motor cortex - Parietal Lobe: reception and evaluation of sensory information except smell, hearing, and vision - Postcentral Gyrus: primary somatosensory cortex - Occipital Lobe: reception and integration of visual input

- Temporal Lobe: reception and evaluation for smell and hearing; memory, abstract thought, judgement - Insula: within the temporal lobe THE CEREBRAL CORTEX: - Surface contains gyri and sulci or fissures - Longitudinal Fissure: separates two cerebral hemispheres - Central Sulcus: separates the frontal and parietal lobes - Lateral Sulcus: separates the temporal and parietal lobes - Parieto-occipital Sulcus: separates the parietal and occipital lobes - Insula: hidden by temporal lobe THE ADULT BRAIN:

CEREBRAL CORTEX:

BRAIN MIDSAGITTAL SECTION:

the

THE PRIMARY MOTOR AREA: - aka the pyramidal system - located in the precentral gyrus THE MOTOR HOMUNCULUS: - size of the motor homunculus is related to the number of motor units of the body region it controls PRIMARY SENSORY AREA: - in the postcentral gyrus - map of the primary sensory cortex showing what region respond to stimulation - regions of the body proximate to each other are also in proximate regions of the cortex - the size of the region of sensory cortex devoted to any region of the body is proportionate to the density of innervation of that region - e.g. fingers and tongue have large cortical areas, whereas the trunk has a smaller area PRIMARY (SOMATO) SENSORY CORTEX: - Sensory Homunculus- receives somatosensory information about touch, pressure, pain, temperature, and the special sense of taste MOTOR, SENSORY AND ASSOCIATION AREAS OF THE CEREBRAL CORTEX:

CHAPTER 12 and 13 (PARTS) tracts, pathways, and cranial nerves, pain perception SPINAL CORD TRACTS: - Tracts: groups of nerve fibers carrying similar information to similiar destinations Anatomically tracts are formed into columns, or fasciculi, in the spinal cord GENERAL ORGANIZATION: - Ascending Tracts: carry sensory information toward the brain, have 3 neurons in series, may have collaterals or connect to interneurons that go to other regions in divergent pathways - Descending Tracts: carry motor information from the brain, have 2 neurons in series, may have collaterals or connect to interneurons that go to other regions in divergent pathways - ALL tracts going to and from the cerebral cortex cross to the opposite side (decussate) before reaching the thalamus. * (thus, the right thalamus and

cerebral cortex control information to and from the left side of the body, and the left thalamus and cerebral cortex control information to and from the right side of the body.) * - This is generally not true for the cerebellar tracts with some exceptions. Most tracts go to the same side of the cerebellum from which they start. - IPSILATERAL and CONTRALATERAL - Most tracts are named from where they start and where they go. SENSORY PATHWAYS: - First Order Neurons: sensory neurons that deliver information to the CNS * (cell bodies are in the DRG) - Second Order Neurons: interneurons in the CNS that synapse with axons from the first order neurons. They can be in nuclei within the spinal cord or brain, and send axons to the thalamus - Third Order Neurons: found in the thalamus, if the sensation will reach conscious awareness (perceived) they send axons to the primary sensory area of the cerebral cortex (on the same side of the body). Collaterals go to other regions (sensory association areas, limbic system, other interpretation areas) CROSSOVER: - The axon of the second order neuron will cross to the opposite side (decussate) of the CNS somewhere along its path. Thus, the thalamus receives input from the opposite side of the body - Third order neurons ascend to the primary sensory cortex on the same side without crossing over SOMATIC SENSORY PATHWAYS: - 3 major pathways carry sensory information, that are further subdivided - Paired sets of tracts on both sides of the spinal cord 1. Posterior (DORSAL) Column Pathway - Fasciculus gracilis

- Fasciculus cuneatus 2. Anterolateral Pathways (SPINOTHALAMIC and OTHERS) 3. Spinocerebellar Pathways POSTERIOR COLUMN PATHWAY: - Carries fine touch, pressure and proprioceptive sensations - AKA Dorsal Column/Medial Lemniscus Pathway - Axons ascend within the: 1. Fasciculus Gracilis: carry information from the inferior portion of the body 2. Fasciculus Cuneatus: carry information from the superior portion of the body, upper limbs, and neck - Second order neurons are in the nucleus gracilis and nucleus cuneatus within the medulla. They decussate and then relay information to the thalamus via a tract called the medial lemniscus ANTEROLATERAL PATHWAY: - Carries poorly localized sensations of crude touch, pressure, pain, itch, and temperature - Second order neurons are in the posterior gray horn of the spinal cord. Axons decussate in the spinal cord and ascend within the spinothalamic tracts * (also the spinoreticular and spinomesencephalic tracts) * SPINOCEREBELLAR PATHWAY: - Carries sensation to the cerebellum concerning proprioception - Proprioception: position of muscles, tendons, and joints - Second order neurons are in the spinal cord - Posterior Spinocerebellar Tracts: uncrossed axons * (ascend on the same side) *, enter cerebellum via inferior peduncle - Anterior Spinocerebellar Tracts: mostly crossed but some uncrossed axons, most crossed axons red-cross in the pons or cerebellum

- Activate purkinje cells on the same side of the cerebellum as they started RETICULAR SYSTEM: - Neuronal cell bodies are diffusely scattered throughout the reticular system, i.e. there are no large nuclei - All sensory information sends collateral fibers to the reticular system - The reticular system sends information to all parts of the cerebral cortex - Reticular Activating System * (RAS) * PAIN: - Pain pathways are highly divergent, send collaterals to the reticular system * (spinoreticular pathway) *, limbic system, hypothalamus, and can activate spinal reflexes - Any sensory neuron can send pain signals if stimulates strong enough via collateral pathways ** ( Substance P, Bradykinin, Endorphins and Enkephalins) ** - Referred Pain

SOMATIC PATHWAYS: - Upper Motor Neuron: cell body lies in a CNS processing center - Lower Motor Neuron: cell body located in a motor nucleus of the brain * (for motor cranial nerves) *, or spinal cord and send axons to skeletal muscles - Each lower motor neuron innervates a single motor unit and cause contraction of a muscle - 3 somatic motor pathways which are subdivided

MOTOR

1. Corticospinal & Cortical Bulbar Pathways 2. Medial Pathways 3. Lateral Pathways - Basal Nuclei and Cerebellum monitor and adjust activity within these pathways - Facilitate or inhibit neurons THE CORTICOSPINAL PATHWAY (PYRAMIDAL SYSTEM): - Starts with pyramidal cells of the primary motor cortex - Provides voluntary skeletal muscle control - Corticobulbar Tracts: terminate at cranial nerve nuclei * (control jaw, eye, face, some neck muscles) * - Corticospinal Tracts: synapse on motor neurons in the anterior gray horns of the spinal cord * (visible along medulla as pyramids) * MEDIAL AND LATERAL PATHWAYS: - Issue motor commands as a result of subconscious processing- indirect (multinational) pathways * (reflex controls) * - There is extensive feedback between these centers and the pyramidal system, so that they work as functional units. Primarily controls gross movements of the trunk and proximal limbs - Upper motor units are in the: 1. Vestibular Nuclei (Vestibulospinal Tracts) 2. Superior and Inferior Colliculi (Tectospinal Tracts) 3. Red Nucleus (Rubrospinal Tract) 4. Reticular Formation (Reticulospinal Tracts) SUMMARY OF MOTOR CONTROL:

DESCENDING (MOTOR) TRACTS IN THE SPINAL CORD:

CRANIAL NERVES: - 12 pairs of cranial nerves - Most attach to the ventrolateral surface of the brainstem near the associated sensory or motor nuclei - They can either be: 1. Sensory (afferent nerves) 2. Motor (efferent nerves) 3. Both (mixed nerves) OLFACTORY NERVES:

- Carry sensory information responsible for sense of smell - Synapse within the olfactory bulb * (which is actually an extension of the cerebrum) * - Only cranial nerve to actually synapse directly with the cerebrum rather than lower brain structures CRANIAL NERVES 2,3,4: - Optic Nerves (2): carry visual information from special sensory receptors in the optic chiasm and optic tracts - Oculomotor Nerves (3): primary source of innervation 4 of the extraocular muscles, the eyelids, and the pupils - Trochlear Nerves (4): innervate the superior oblique muscles CRANIAL NERVES 5 & 6: - Trigeminal Nerves (5): mixed nerves with ophthalmic, maxillary and mandibular branches - Abducens Nerves (6): innervates the lateral rectus muscles of the eye

scalp, face, the

CRANIAL NERVE 7: Facial Nerves (7): mixed nerves that control muscles of the face and provide pressure sensations over the and receive taste information from tongue

CRANIAL NERVES 8 & 9: - Vestibulocochlear Nerves (8): * (Acoustic or Auditory Nerve) * - Vestibular Branch: monitors balance, position and movement

- Cochlear Branch: monitors hearing - Glossopharyngeal Nerves (9): mixed nerves that innervate the tongue and pharynx, control the action of swallowing, and receive information from tongue and pharynx and the carotid sinus and carotid body CRANIAL NERVE 10: - Vagus Nerve (10): mixed nerve, widely distributed to internal organs, vital to the autonomic control of visceral function, and part of the parasympathetic division

CRANIAL NERVES 11 & 12: - Spinal Accessory Nerves (11): * (Accessory Nerve) * has origins in spinal cord - Internal Branches: innervate voluntary swallowing muscles of the soft palate and pharynx - External Branches: control muscles associated with the neck and pectoral girdle - Hypoglossal Nerves (12): provide voluntary motor control over tongue movement

PARTIAL CHAPTER 13 RECEPTORS AND REFLEXES SENSORY RECEPTORS: - Receptors are specialized cells or cell processes that monitor specfic conditions (respond to stimului) - Act as the interface between the CNS and the internal and external enviorments - Sensation: arriving information into the CNS - Perception: awareness of a sensation - Not all sensations are percieved - Neural inout must go to the primary sensory sreas for conscious awareness RECEPTOR CLASSIFICATION: - Exteroceptors: provide information about the external enviornement - Interoceptors: provide information about visceral organs and functions - Proprioceptors: provide information about positions and tension of the joints and skeletal muscles CLASSIFICATION OF RECEPTORS: - Receptors can also be classified based on the type of stimulus they respond to

- Nociceptors: pain - Thermoreceptors: temperature - Mechanorecptors: physical distoration - Chemoreceptors: chemical concentrations - Photoreceptors: light SENSORY RECEPTORS: - Nerve fiber fire when an action potential is generated regardless of what caused it. Thus, they are non-specific - Specifity comes from specialized receptors - Receptor cells are generaly sensitive to limited types of stimuli * (modality) * known as receptor specifity - Each receptor cell monitors a specfic receptive field - The larger the receptive field the less precise localization is RECEPTORS AND RECEPTIVE FIELDS:

RECEPTOR FIELDS AND 2 POINT DISCRIMINATION:

INTERPRETATION OF SENSORY INOFRMATION: - *** Nerve fibers are non-specific ***, but they go to specifc regions of the brain along with specfic tracts or bund;es - Information is interpreted based on the labeled line that it travels as to what type of sensation it is * (qualitative processing) * - True sensations cannot be distinguised from false sensations - All other characteristics of a stimulus * (strength, durations, variability, etc) * are conveyed by the frequency and pattern of the action potentials * (quantitative processing) * RECEPTORS: - Tonic Receptors: always active, frequency of firing determines information, and slow to adapt - Phasic Receptors: normally inactive, give a burst of activity when stimulated, and provide information about the intensity and rate of change of a stimulis - Combined Receptors ADAPTATION: - Reduction in sensitivy of a receptor in the presence of constant stimulus - Peripheral Adaption: occurs at the level of the receptor, and reduces sensory information entering the CNS - Fast-Adapting Receptors: phasic receptors * (temperature) * - Slow-Adapting Receptors: tonic receptors * (pain, proprioception) * - Central Adaption: occurs within the CNS and often involves inhibitory interneurons within the pathway - CNS can inhibit sensory pathways for example to “filter noise” - Reduces information reachinf the cerebral cortex, awareness is reduced even though the recptors are still active, responses may still occur via lower level circuits - CNS output can also facilite transmission * ( increase sensory transmission) *

SENSORY RECEPTORS: - Free Nerve Endings: dendrites, not protected by accessory structures, sensitive to many stimuli * (pain, temperature, pressure, trauma) * - Comples Receptors: often not neural cells, merkel cells, rod and cones MECHANORECEPTORS: - Sensitive to distorition of thier membrane - Mechanically sensitive ion channels - Tactile Receptors (6 types): touch, pressure, vibration - Touch: shape and texture - Pressure: mechanical distortion - Vibration: pulsing or oscillating pressure - Barorecptors: monitior pressure changes - Proprioceptors (3 groups): joint and muscle movement, position and location

TACTILE RECEPTORS: - Crude Touch and Pressure: have large receptor fields - Tactile Receptors: more narrow fields provide more inofrmation 1. Free Nerve Endings 2. Root Hair Plexus: rapid respond to movement 3. Tactile Discs (Merkel Discs): fine touch, myelinated fibers, found in the epidermis, attached to a free nerve ending 4. Tactile Corpuscles (Meissner’s Corpuscles): fine touch and pressure, low frequency vibrations. Myelinated fibers adapt within 1 seconf after contact 5. Lamellated Corpuscles (Pacinian Corpuscles): large structures, deep pressure, fast adapting so more sensative to vibrations. Seen in viscera such as mesentaries, in the pancreas, urethra, and urinary bladder, as well as skin 6. Ruffini Corpuscles: pressure and distortion of skin proprioception, located in deep dermis, show little adaption

- Itch and tickle sensations use free nerve endings PROPRIOCEPTION: - Muscle spindle - Golgi tendon organs - Joint kinesthetic receptors - Stretch receptors or joint pressure CHEMORECEPTORS: - Chemoreceptors of the general senses do not send information to the primary sensory cortex. Thus, there is no concious awareness * (sensation wihtout perception) * - Exhibit peripheral adaption after a few seconds and may exhibit central adaptation - Carotoid bodies and Aortic bodies are sensitive to pH, CO2 and O2 - Chemoreceptors may respond to chemical released by damaged tissue

SUMMARY SLIDES:

REFLEXES: - Reflexes: rapid automatic responses to stimuli - Neural reflex involves sensory fibers to CNS and motor fibers to effectors ...