Ch 12 - Central Nervous System PDF

BIOL243 – HUMAN ANATOMY & PHYSIOLOGY I Charles Smith, PhD CSCS HUMAN ANATOMY & PHYSIOLOGY Ch. 12 – Central Nervous System CENTRAL NERVOUS SYSTEM Brain & Spinal Cord Both begin as a neural tube during embryological development Anterior tube end expands into: Fo...

BIOL243 – HUMAN ANATOMY & PHYSIOLOGY I Charles Smith, PhD CSCS HUMAN ANATOMY & PHYSIOLOGY Ch. 12 – Central Nervous System CENTRAL NERVOUS SYSTEM Brain & Spinal Cord Both begin as a neural tube during embryological development Anterior tube end expands into: Forebrain Midbrain Hindbrain These later differentiate into the major regions of the brain Cerebral hemispheres Diencephalon Brainstem Cerebellum Posterior tube end becomes spinal cord Central cavity of tube becomes the ventricles which house cerebrospinal fluid (CSF) THE CEREBRUM Superior portion of the brain 83% of brain’s total mass Arises from the telencephalon Right & Left halves (hemispheres) separated by (deep) longitudinal fissure Totality of cerebrum separated from cerebellum by (deep) transverse fissure Has a number of ridges (gyri) and shallow grooves (sulci) Increase brain surface area Maximizes its volume within the space Facilitates inter-regional communication by condensing things a bit Divided into 4 lobes (Frontal, Parietal, Occipital, Temporal) corresponding to overlaying cranial bones Insula: deep, interior lobe surrounding diencephalon CEREBRAL REGIONS 3 Basic Regions contained within each hemisphere: 1. Cerebral Cortex Superficial gray matter Divided into functional areas of brain 2. White Matter Internal white matter Contain the CNS’s neural tracts 3. Basal Nuclei (Basal ganglia) Gray matter islands within white matter Primarily involved in motor control CEREBRAL CORTEX 3 types of functional areas: 1. Motor 2. Sensory 3. Association Activity in a hemisphere largely corresponds to stimuli going to/from the opposite side of the body i.e., your left hemisphere “controls” your right side Over time, tasks get lateralized to a hemisphere We use both sides for most tasks, but one side gets more specialized and dominates Hemisphere dominance often corresponds to handedness 90% people right-handed (left hemisphere) dominant Lefties really are “special”: more bilateral activation & patterns in many ways different than righties Conscious behavior involves entire cortex in some way No, you don’t only use “10% of your brain” But that may be all we are consciously aware of MOTOR AREAS OF CEREBRAL CORTEX Voluntary movement control 1. Primary motor cortex (M1) or precentral gyrus Anterior to central sulcus In charge of precise, skilled, skeletal muscle movements 2. Premotor cortex (pMC) Anterior to M1 In charge of “planning” movements Especially learned, repetitious, patterned motor skills Relays assisting information from cognitive areas in frontal cortex 3. Broca’s Area Speech motor area (generates speech patterns) Present only on dominant hemisphere Damage to these areas (i.e., via stroke) can be problematic Damage to M1: to paralysis of musculature controlled by that hemisphere (hemiplegia) Damage to pMC: won’t impact muscle function but can affect performance of learned tasks Damage to Broca’s area: impaired speech production (Broca’s aphasia) Skills can be relearned with rehab Brain has to “reprogram” other areas to take over SENSORY AREAS OF CEREBRAL CORTEX 1. Primary Somatosensory Cortex (S1) or postcentral gyrus Immediately posterior to central sulcus & M1 Receives general sensory information from skin & proprioceptors Aid with spatial discrimination: body position in space & what body region is being stimulated Communicates with pMC to improve/update motor pattern(s) 2. Somatosensory Association Area (SA) Comprises remainder of parietal lobe posterior to S 1 Integrates sensory input from S1 Helps sense size, texture, relationship of parts of an object Communicates with frontal and premotor cortices Use feedback to enhance task learning, improve motor patterns Partly contains Wernicke’s Area Overlaps with auditory association area in temporal lobe Responsible for the understanding of speech & written language People with Wernicke’s Aphasia are capable of talking/writing but will often do so in gibberish SENSORY AREAS OF CEREBRAL CORTEX 3. Primary Visual Cortex & Visual Association Area Occipital lobe Primary Visual on most posterior aspect Receives information from retinas (Primary) and uses past experience to interpret stimuli (Association) 4. Primary Auditory Cortex & Auditory Association Area Superior margin of temporal lobe (near lateral sulcus) Primary interprets sound information (i.e., pitch, volume, location); Association stores that information as memory 5. Vestibular Cortex Insula and deeper portions of parietal lob Receives & integrates information from the inner ear to regulate balance 6. Olfactory Cortex Medial temporal lobe Receives & integrates information from olfactory sensors in nose (odors) Also aids in the storage of those smells to memory 7. Gustatory Cortex Insula deep to temporal lobe Receives information from tastebuds on tongue Works with olfactory cortex to perceive taste (try to taste without smell) 8. Visceral Sensory Area Posterior to gustatory cortex Responsible for visceral sensation (i.e., “full” stomach, bladder, etc.) FRONTAL AREAS OF CEREBRAL CORTEX 1. Prefrontal Cortex or Anterior Association Area Most complicated cortical region Involved with intellect, cognition, recall, personality Also holds working memory for ideas, judgement, reasoning, persistence, planning Requires feedback from social environment to develop Tumors or lesions in this area may cause mental & personality disorders i.e., loss of judgment, attentiveness, inhibitions Affected people may be oblivious to social restraints, become careless about selves, take risks 2. Frontal Cortex or Posterior Association Area Large region encompassing portions of frontal, parietal, & occipital lobes Uses and integrates information from motor, sensory, and visual cortices Recognizing patterns, faces Localization in space Aiding how we manipulate in that space LIMBIC AREA OF CEREBRAL CORTEX 1. Limbic Association Area Crosses over into diencephalon encompassing parts of thalamus, hypothalamus, hippocampus & amygdala Amygdala linked with fear response and emotional responses to odor Hippocampus linked with memory Essentially gives us the “emotional impact” to give a moment or experience meaning enough to establish a powerful memory BASAL NUCLEI (BASAL GANGLIA) Caudate Nucleus, Putamen, Globus Pallidus Caudate & putamen together make up the striatum Basal ganglia receive input from the entire cerebral cortex Largely involved in movement control Functions seem to overlap with those of cerebellum Seem to have great importance in the initiation, termination, and regulating intensity (scaling) of movements Also seem to have a role in cognition & emotion i.e., filtering out incorrect or inappropriate responses DIENCEPHALON 1. Thalamus Major waypoint for sensory information going to cortices Often where those tracts switch to proper side (decussate) Overall, helps mediate sensation, motor activities, sleep/wake cycle, learning, memory 2. Hypothalamus Inferior to thalamus Major visceral control center: key to maintaining homeostasis BP, HR, GI function Emotional responses (with limbic system): fear, rage, pleasure, sex drive, etc. Body temperature Hunger/satiety Hormone function: directly secretes some; stimulates the pituitary for others Water balance 3. Epithalamus Pineal gland: secretes melatonin for sleep/wake regulation BRAIN STEM Survival Control Each part controls something without which you cannot (feasibly) live Associated with 10 out of 12 cranial nerve pairs 3 Regions: Midbrain Between diencephalon and pons Contains the corpora quadrigemina (superior & inferior colliculi) which are involved with head movement, visual stimuli, and auditory stimuli Pons Between midbrain and medulla oblongata Origin point for cranial nerves V – VII Assists medulla with maintaining respiratory rate Medulla Oblongata Blends into spinal cord at foramen magnum Origin point for cranial nerves IX – XII Works with hypothalamus to regulate autonomic functions Cardiovascular center: force & rate of heart contractions; blood pressure regulation Respiratory center: rate and depth of breathing (with pons) Others: vomiting, hiccups, swallowing, coughing, sneezing CEREBELLUM Dorsal to pons & medulla; inferior to cerebral cortex Separated by transverse fissure Processes input from cortex, brain stem, and sensory receptors Facilitates movement precision, coordination, & balance control Cerebellar Ataxia: inability to coordinate muscle movement due to disease or injury to cerebellum Movements appear to be very awkward & jerky Will also impact speech and swallowing Can arise from head trauma, stroke, tumors, MS, alcohol abuse Cerebral Palsy: group of conditions affecting movement & posture Often caused by damage to developing brain (often before birth Symptomologies vary dramatically Muscles being too limp to too stiff (rigidity) Movements being exaggerated (spastic) to uncontrollable (tremoring) And more MENINGES Cover and protect the CNS Protect blood vessels and enclose the venous sinuses Contain cerebrospinal fluid (CSF) 3 Layers: Dura mater (most superficial) Two layers of fibrous connective tissue Mostly fused together but will separate in certain areas to make dural venous sinuses for blood to leave brain Epidurals are applied to the space superficial to this Arachnoid mater Has spiderweb-like extensions Separated from dura mater by subdural space Subarachnoid space sits between this layer & pia mater Contains CSF and largest blood vessels of the brain Pia mater (deepest) Delicate connective tissue clinging tightly to brain (the brain’s shrink wrap) Has many tiny blood vessels that feed the brain Meningitis: inflammation of the meninges Either viral, bacterial, fungal, or parasitic cause Determined via lumbar puncture & CSF sample If left untreated can cause brain inflammation (encephalitis) → death CEREBROSPINAL FLUID (CSF) Liquid cushion of constant volume surrounding brain Gives CNS structures buoyancy Protects CNS from blows and other traumas Nourishes brain & carries chemical signals Ventricles: CSF-filled chambers continuous with one another & central canal of spinal cord Lined with ependymal cells which control CSF production Supply CSF into deeper structures of the brain Hydrocephalus: obstruction blocks CSF circulation or drainage causing increased pressure Shunt must be installed to direct CSF from ventricles to abdominal cavity Ventriculomegaly: enlarged ventricles possibly indicated excess CSF In utero: may be due to genetic condition or infection Will also be seen in post-stroke patients on side of lesion TRAUMATIC BRAIN INJURIES (TBI) Concussion: “brain bruise” Second-impact syndrome: compounding of trauma caused by second successive impact i.e., blow to head then second hit from ground impact Having one concussion puts you at higher risk for another Hemorrhages/Hematomas: bleeding In epidural, subdural, subarachnoid meningeal spaces Cerebral Edema: swelling of the brain associated with TBI Treated by either removing part of skull allowing brain to expand or drilling a Burr hole (drain CSF allowing brain space) Chronic Traumatic Encephalopathy (CTE): linked to repeated head injuries causing nerve cells to die & degenerate Can trigger severe behavioral/mood changes/disorders and cognitive & motor decline Only way to diagnose is post mortem Notable cases: Junior Seau (football), Aaron Hernandez (football), Chris Benoit (WWE) CEREBROVASCULAR INCIDENTS (CVA) Stroke Ischemia: tissue becomes deprived to blood leading to tissue death Typically caused by blockage (clot) in cerebral artery Can also be hemorrhagically caused Transient Ischemic Attacks (TIA): temporary episodes of reversible central ischemia Usually from carotid artery atherosclerosis Mnemonic to identify stroke: FAST Face – facial weakness Can you smile? Has face drooped (i.e., Bell’s palsy) Arms – arm weakness Can you raise both arms evenly? Speech – impaired speech Is speech clear & understandable? Slurred? Time – time is the most critical factor Earlier detection, earlier treatment, likely better long-term outcome DEGENERATIVE BRAIN DISORDERS Alzheimer’s Disease (AD): progressive, degenerative disease resulting in dementia Memory loss, short attention span, disorientation, language loss, irritability, moodiness, confusion, hallucinations Brain cells die, brain shrinks noticeably on CT and fMRI Notable case: Gene Wilder (actor); Barbara Walters (TV journalist) Parkinson’s Disease (PD): degeneration of dopamine- releasing neurons in substantia nigra Resulting tremors at rest, shuffling gait, speech difficulty Notable Case: Michael J. Fox (actor); Ian Holm (actor) SPINAL CORD Enclosed in the vertebral column extending from foramen magnum to L1/L2 vertebra Terminating structure the cone-like conus medullaris with filum terminale extending to coccyx Cauda equinae: collection of nerve roots at inferior end of vertebral canal Facilitates two-way brain-body communication Spinal nerves are part of PNS Attach to cord at 31 paired roots Major reflex center Many of our reflex response are initiated & completed at local portion of spinal cord SPINAL CORD (CROSS- SECTION) Gray matter areas are mirrored on either side of center Cross-section resembles letter “H” or a butterfly Dorsal Horns: sensory input (afferent) Dorsal Roots: sensory axons entering spinal column Dorsal Root Ganglia: collections of sensory axons near where dorsal root intersects with dorsal horn Ventral Horns: motor output (efferent) Ventral Roots: motor axons exiting spinal cord Dorsal & Ventral roots fuse together outside spinal cord to make spinal nerves SPINAL CORD (CROSS- SECTION) White matter comprised of myelinated & unmyelinated fibers Allows communication between Parts of the spinal cord Spinal cord to brain Communication runs in 3 directions Ascending (sensory, afferent): toward higher brain centers Descending (motor, efferent): from brain to spinal cord OR to lower cord levels Transverse (commissural): from one side of spinal cord to the other Mostly Ascending and descending fibers make up white matter areas Funiculi – bundle of fiber tracts; named based upon position on spinal cord SPINAL CORD TRAUMA Paresthesia: abnormal sensation (often tingling); caused by damage to dorsal roots or sensory tracts Paralysis: loss of motor function due to damage to ventral roots or ventral horn Flaccid Paralysis: spinal cord or ventral roots injured; nerve impulses cannot reach muscles rendering them limp Spastic Paralysis: upper motor neurons of motor cortex damaged; spinal neurons remain intact creating reflexive contractions but no voluntary control SPINAL CORD TRAUMA Transection (cross-sectioning) of spinal cord at any level results in motor & sensory losses in regions inferior to injury i.e., if the spinal cord is cut at T 5, nerves from T6 and below will lose function Paraplegia: transection between T1 & L1; results in loss of function of lower limbs i.e., Joe Swanson from Family Guy Quadriplegia: transection in cervical region; results in loss of function in all extremities i.e., Christopher Reeve (actor) Hemiplegia: loss of function of a single side of the body Atypical in spinal cord injuries; more common in brain injury Spinal Shock: transient period of functional loss following a spinal cord injury Even if cord not transected, function will still be impaired i.e., swelling See a loss in all reflex activity caudal to the injury site i.e., bowel & bladder function, muscle tone & contractility, BP drops If function does not restore within 48 hrs, paralysis may be permanent SPINAL CORD DISORDERS Poliomyelitis: from poliovirus destroying ventral horn motor neurons Early symptoms: fever, headache, muscle pain, muscle weakness Later symptoms: paralysis, muscle atrophy Vaccination has nearly eradicated this disease Notable Case: Franklin Delano Roosevelt (president) Amyotrophic Lateral Sclerosis (ALS): ventral horn motor neurons gradually deteriorate and waste away Results in an (eventual) total loss of muscle function (except bladder, digestive, and sexual function) Typically begins with distal appendages and move proximally over time Notable Cases: Lou Gehrig (baseball), Prof. Stephen Hawking (physicist) CENTRAL NERVOUS SYSTEM SUMMARY CNS is comprised of the brain and spinal cord Brain is segmented into the Cortex, Diencephalon, Cerebellum, & brain stem Cortical regions named based upon cranial bones covering them Each have different functional areas (i.e., motor cortices, sensory cortices, visual cortex, etc.) Diencephalon is deep to cortex and superior to brain stem Holds the thalamus, hypothalamus, and epithalamus which are key waypoints for motor and sensory tracts and maintenance of homeostasis Cerebellum communicates with the cortical regions to coordinate movement patterns Brain stem is responsible for base, survival functions like breathing rate, heart rate, and homeostasis regulation Damage inflicted upon the brain (i.e., TBI, stroke, degenerative disease) will impair function based upon location of injury and/or tracts affected Spinal cord travels the length of the spinal column starting from the base of the medulla oblongata Motor and sensory nerves protrude laterally from the cord at each vertebra Facilitates communication to the brain and between different areas of the spinal cord Damage or degeneration of the spinal cord essentially cuts off communication to and from the brain SAMPLE QUESTIONS 1. The precentral gyrus is also known as what cortex? 2. The epithalamus releases what neurotransmitter? 3. Damage to the cerebellum causing clumsy, uncoordinated movements is called what? 4. What does the “FAST” acronym for stroke mean? 5. The white matter bundles of nerve tracts are referred to as what?  COPYRIGHT © Pearson Edited by Charles Smith, PhD CSCS 2024