The Brain and Spinal Cord Notes PDF

THE BRAIN ​ Major regions of the brain ○​ Cerebrum ​ Largest component of brain ​ Controls higher mental functions → conscious thought & intellectual functions ​ Divided into 2 hemispheres → right & left cerebral hemisphere...

THE BRAIN ​ Major regions of the brain ○​ Cerebrum ​ Largest component of brain ​ Controls higher mental functions → conscious thought & intellectual functions ​ Divided into 2 hemispheres → right & left cerebral hemisphere ​ By longitudinal fissure ​ Connected by corpus callosum ○​ Diencephalon ○​ Midbrain ○​ Pons ○​ Medulla oblongata ○​ Cerebellum ​ Cross section of the cerebrum ○​ Gray matter ​ Thin outer layer ​ AKA cerebral cortex ​ Contains neuron cell bodies ○​ White matter ​ Inner layer ​ Contains nerve fibres ○​ Cerebral nuclei (basal nuclei) ​ Areas of gray matter in central white matter ​ Structure of cerebral hemisphere ○​ Frontal lobe ​ Front of forehead, bordered by precentral gyrus ○​ Parietal lobe ​ Towards middle of the head, bordered by the postcentral gyrus and parieto-occipital sulcus ○​ Temporal lobe ​ Middle bottom of the brain ○​ Occipital lobe ​ At the back of the head bordered by the parieto-occipital sulcus ​ Sulci, gyri & lobes of cerebrum ○​ Contains numerous folds & depressions ​ Gyri ​ Elevated ridges that increase SA of cortex ​ Singular is gyrus ​ Sulci ​ Shallow depressions ​ Singular is sulcus ​ Fissures ​ Deep grooves  ○​ Central sulcus ​ Separates frontal lobe & parietal lobe ​ Precentral & postcentral gyrus ○​ Lateral sulcus ​ Separates frontal lobe & temporal lobe ○​ Parieto-occipital sulcus ​ Separates parietal lobe & occipital lobe ​ Functional areas of the cerebrum ○​ Each hemisphere: ​ Receives sensory info from opposite side of body ​ Sends motor commands to opposite side of body ​ Has specific areas w specific functions ○​ Motor cortices ​ Primary motor cortex ​ Located in precentral gyrus of frontal lobe ​ Directs voluntary movement ​ Primary sensory cortex ​ Located in postcentral gyrus of parietal lobe ​ Receives somatic sensory info ○​ Eg touch, pressure, pain, temperature ○​ Special sensory cortices ​ Visual cortex (occipital lobe) ​ Receives visual info ​ Auditory cortex (temporal lobe) ​ Received info about hearing ​ Olfactory cortex (temporal lobe) ​ Receive info about smell ​ Gustatory cortex (frontal lobe) ​ Receive info about taste ○​ Association areas ​ Located adjacent to sensory, motor areas ​ Consists of somatic motor association area (premotor cortex) and somatic sensory association area ​ Somatic motor association area (premotor cortex) ○​ Coordinates learned movements ​ Somatic sensory association area ○​ Interpret sensory info ○​ Association areas for vision, hearing ○​ Higher order centres ​ Integrative centres receiving info from many association areas ​ Direct complex motor or analytical activities ​ Consists of general interpretive area (GIA), speech centre and prefrontal cortex  ​ General Interpretive Area (GIA) ○​ AKA wernicke’s area ○​ Present in only 1 hemisphere (usually left) receives info from all sensory association areas ○​ Coordinates access to complex visual & auditory memories ○​ Damage → results in inability to interpret what is read/ heard ​ Speech centre ○​ Connected to GIA in same hemisphere ○​ Coordinates all vocalisation functions like breathing pattern for speech ○​ Damage → results in difficulty with speech ​ Prefrontal cortex ○​ Coordinates information from sensory association areas of entire cortex ○​ Performs abstract intellectual activities → predicting consequences of actions, feelings of frustration ○​ Hemispheric lateralization ​ Basically your dominant side is handled by the opposite side of the hemisphere in the brain ​ In a right handed person, ​ Writing taken care of the left hemisphere, same as speech centre and GIA (language & mathematical calculations) ​ Non-dominant hemisphere, spatial visualization & analysis ​ Right side of visual cortex goes to left cerebral hemisphere and vice versa ​ Basal nuclei (cerebral nuclei) ○​ Masses of gray matter ​ Embedded in white matter of cerebrum ○​ Functions: ​ Involved in subconscious control of skeletal muscle tone & coordination of learned movement patterns ​ Limbic system ○​ Functional group: ​ Olfactory cortex ​ Basal nuclei ​ Tracts between cerebrum & diencephalon ○​ Functions: ​ Establishes emotional states ​ Facilitates memory storage & retrieval ​ Makes you want to do things (drive) ​ Diencephalon ○​ Integrates sensory info & motor commands ○​ Consists of: ​ Epithalamus ​ Forms root of diencephalon ​ Anterior part → contains choroid plexus ​ Posterior part → contains pineal gland secreting melatonin & hormone regulating day-night cycles ​ Thalamus (picture inserted beside) ​ Round mass of thalamic nuclei ​ Functions: ○​ Final relay point for all ascending sensory info except smell ○​ Coordination of voluntary & autonomic functions ​ Hypothalamus ​ Located below thalamus, above pituitary gland ​ Contains important control & integrative centres ​ Functions: ○​ Subconscious control of skeletal muscles → eg rage, pain, sexual arousal ○​ Adjusting activities of autonomic centres in pons, medulla → eg HR, BP, breathing, digestion ○​ Coordination of activities of neuron system & endocrine system ○​ Secretion of hormones ○​ Behavioral drives associated w thirst centre & hunger centre ○​ Regulation of body temperature ○​ Coordination of day-night cycles of activity ​ Brain stem ○​ 3 major regions: ​ Midbrain ​ Superior & inferior colliculus ○​ 2 pairs of colliculus on posterior surface ​ Contains sensory nuclei associated with visual reflexes (superior colliculus) & auditory reflexes (inferior colliculus) ​ Cerebral aqueduct ○​ Passageway for cerebrospinal fluid in central cavity ​ Cerebral peduncles ○​ On ventrolateral surfaces ○​ Contains bundles of descending motor fibres from cerebrum to other parts of brain ​ Reticular activating system (RAS) ○​ Required for attentiveness & wakefulness  ​ Midbrain nuclei (e.g. substantia nigra, red nucleus) ○​ For involuntary movements ​ Nuclei for cranial nerves III, IV ​ Pons ​ Links cerebellum w brain stem & spinal cord ​ Contains → respiratory centres & nuclei for cranial nerves V-VIII ​ Medulla oblongata ​ Connects brain to spinal cord ​ Functions ○​ Relays information between spinal cord & brain ○​ Contains: ​ Autonomic centres ​ Vasomotor centre, respiratory centres ​ Reflex centres ​ Coughing, vomiting, sneezing, swallowing ​ Nuclei for cranial nerves IX-XII ​ Cerebellum ○​2nd largest part of brain ○​2 hemispheres → right & left; is connected by the vermis ○​Cerebellar peduncles → contains tracts linking cerebellum w other parts of CNS ○​Has 2 important functions:​ ​ Adjusting postural muscles → maintain balance ​ Programs , fine-tunes & smoothens voluntary & involuntary movements; does not initiate movement ○​ Damage of cerebellum → causes ataxia; disturbance in balance & gait ​ The meninges ○​ 3 layers of protective membranes ○​ Cover brain & spinal cord completely ○​ Arrangement: ​ Dura mater (outermost covering) ​ Tough fibrous membrane covering brain & spinal cord ​ Structure slightly different in cranial cavity & vertebral column ​ In cranial cavity ○​ Consists of 2 layers: ​ Outer layer → fused to periosteum of skull ​ Inner layer → extends into cranial cavity forming dural folds ○​ Support & stabilise brain ○​ Contain dural sinuses (dural blood)​ ​ In vertebral column ○​ 1 layer; epidural space ○​ Between vertebrae & dura ○​ Contains loose connective, blood vessels & fats ○​ Used for epidural block  ​ Arachnoid matter (middle layer) ​ Thin, delicate network of fibres → like spider-webs ​ Separated from dura by subdural space → contains lymph ​ Separated from pia by subarachnoid space → contains cerebrospinal fluid ​ Pia matter (innermost) ​ Thinnest membrane ​ Closely applied onto brain surface ​ Contains cerebral vessels ​ Clinical note: meningitis ​ Inflammation of meninges ​ Caused by bacteria & viruses ​ Ventricles of brain ○​ 4 internal cavities → contains cerebrospinal fluid; connected by openings, channels ○​ 2 lateral ventricles ​ 1 in each cerebral hemisphere ​ Connect through interventricular foramen ○​ Third ventricle of diencephalon ​ Connects via cerebral aqueduct ○​ Fourth ventricle posterior to pons ​ Continues as central canal in spinal cord ​ Cerebrospinal fluid ○​ Clear watery fluid surrounding CNS → 150ml ○​ Circulates through cavities of CNS & subarachnoid space ○​ Production → @ choroid plexuses (network of ependymal cells & capillaries) of the ventricles ○​ CSF CIRCULATION ​ Circulates from lateral ventricle to 3rd ventricle via interventricular foramen & from 3rd ventricle to 4th ventricle via cerebral aqueduct ​ Exits ventricles via median & lateral apertures → flow around the brain & spinal cord in subarachnoid space ​ Also goes down central canal of spinal cord ○​ CSF REABSORPTION ​ @ arachnoid granulations ​ Extensions of arachnoid matter from subarachnoid space to dura sinuses ​ Flows into dura sinuses & into venous circulation ○​ CSF FUNCTIONS ​ Supports brain ​ Cushions brain & delicate neural structures ​ Maintains chemical stability & remove metabolic waste from CNS through blood brain barrier  ○​ CLINICAL NOTES ​ Lumbar puncture or spinal tap ​ Puncture made @ subarachnoid space between L3-L4 ​ Sampling of CSF for clinical info about CNS injuries, infections/ diseases ​ Hydrocephalus ​ Rate of CSF reabsorption < rate of production of CSF ​ Obstruction of CSF flow ​ Blood supply of brain ○​ Brain highly active organ → supplied by 2 pairs of arteries → internal carotid arteries & vertebral arteries ○​ Internal carotid system ​ Internal carotid arteries enter skull via carotid canal and main branches are anterior cerebral artery and middle cerebral artery ​ Anterior cerebral artery ​ Supplies frontal poles of cerebrum & medial, superior surfaces of cerebral hemisphere (except occipital lobe) ​ Functional areas: ○​ Gustatory cortex ○​ Motor, sensory cortices of lower limbs ​ Middle cerebral artery ​ Supplies lateral surface of cerebral hemisphere, cerebral nuclei & internal capsule ​ Functional areas: ○​ Motor, sensory cortices ○​ Auditory & olfactory cortices ○​ Language areas (wernicke’s & broca’s areas) of dominant hemisphere. ○​ Vertebrobasilar system ​ Vertebral arteries enter skull via foramen magnum and supplies ​ Spinal cord (cervical) ​ Brain stem ​ Cerebellum ​ Occipital lobe ​ Main branches: ​ Spinal arteries ​ Basilar artery ​ Cerebellar arteries ​ Posterior cerebral artery ○​ Posterior cerebral artery ​ Branch of basilar artery ​ Supplies occipital lobe, diencephalon & midbrain ​ Circle of willis ○​ Arterial ring on ventral surface of brain ○​ Connects internal carotid & vertebrobasilar systems ○​ Significance → provides alt route in event of occlusion of any of these arteries ​ Formation of circle of willis ○​ Internal carotid artery ○​ Anterior cerebral artery ○​ Posterior cerebral artery ○​ Anterior communicating artery ○​ Posterior communicating artery ○​ Venous drainage: ​ Veins of the brain → do not accompany arteries & not have valves ​ Drain into dural venous sinuses → in dura layers → eg superior sagittal sinus ​ Drain into internal jugular veins in neck to superior vena cava  THE SPINAL CORD ​ Gross anatomy of spinal cord ○​ Conus medullaris ​ Conical part below lumbar enlargement ○​ Cauda equina ​ Nerve roots extending from conus medullaris ○​ Consists of 31 segments ​ 8 cervical ​ 12 thoracic ​ 5 lumbar ​ 5 sacral ​ 1 coccygeal ○​ Each segment has similar structural features ​ Sectional anatomy of spinal cord ○​ Posterior median sulcus ​ Shallow groove on dorsal surface ○​ Anterior median fissure ​ Deeper groove on anterior surface ○​ Central canal ​ Filled with CSF ○​ Each spinal segment has pair of: ​ Dorsal roots ​ Contains axons of sensory neurons ​ Dorsal root ganglia ​ Contain cell bodies of sensory neurons ​ Ventral roots ​ Contains axons of CNS motor neurons ​ Dorsal + ventral roots = spinal nerves ​ Spinal nerves → mixed nerves ​ Have both sensory & motor fibres ○​ Gray matter ​ Forms “H” around central canal ​ Contains neuron cell bodies ​ Has projections (gray horns) ○​ Posterior gray horn ​ Contains sensory nuclei ○​ Anterior gray horn ​ Contains somatic motor nuclei ○​ Lateral gray horn ​ Found only in thoracic & lumbar segments ​ Contains visceral (autonomic) motor nuclei ○​ Gray commissures ​ Contains axons that cross from 1 side of spinal cord to other  ​ Connect horns on either side of spinal cord ○​ White matter ​ More superficial ​ Divided into 3 columns containing bundles of sensory (ascending) & motor (descending) nerve fiber tracts ​ Posterior white columns ​ Anterior white columns ​ Lateral white columns ​ Functions of spinal cord ○​ Passageway for info travelling between brain & body ○​ Controls spinal reflexes ​ Clinical note: spinal injuries ○​ Causes ​ Physical trauma to spinal cord ​ Spinal meningitis ​ Herniated intervertebral discs ○​ Clinical symptoms ​ Loss of sensation (anaesthesia) & voluntary movement (flaccid paralysis) ​ Damage @ C4/ C5 vertebra → loss of sensation & motor control of upper & lower limbs (quadriplegia) ​ Damage to thoracic vertebrae → loss of motor control of lower limbs (paraplegia) ​ Spinal nerves ○​ Found in 31 pairs grouped acc to region of vertebral column: ​ 8 pairs of cervical nerves → C1-C8 ​ 12 pairs of thoracic nerves → T1-T12 ​ 5 pairs of lumbar nerves → L1-L5 ​ 5 pairs of sacral nerves → S1-S5 ​ 1 pair of coccygeal nerve, Co1 ​ Nerve plexuses ○​ Networks of major nerve trunks ○​ Cervical plexus ​ Innervates muscles of neck & diaphragm ○​ Brachial plexus ​ Innervates pectoral girdles & upper limbs ○​ Lumbar & sacral plexus = lumbosacral plexus ​ Innervates pelvic girdle ​ Peripheral nerves ○​ Arise from nerve plexuses ○​ Contains both sensory & motor nerve fibres eg sciatic nerve ○​ Peripheral neuropathies  ​ Regional losses of sensory/ motor function as result of nerve trauma/ compression ​ Reflexes ○​ Rapid automatic motor responses to specific stimuli → always produce same response ○​ Preserves homeostasis through -ve feedback ○​ Reflex arc refers to wiring of single reflex ​ Begins @ sensory receptor & ends @ effector ​ 5 steps in natural reflex arc ○​ Arrival of stimulus, activation of receptor ○​ Activation of sensory neuron ○​ Information processing in CNS ○​ Activation of motor neuron ○​ Response of peripheral effector ​ Spinal reflexes ○​ Coordinated within spinal cord → involves synapses ○​ Monosynaptic reflexes ​ Simple reflexes w 1 synapse ​ Most rapid motor response of nervous system ​ Sensory neuron synapses directly w motor neuron → eg stretch reflex ○​ Polysynaptic reflexes ​ Complex reflexes with interneurons\ ​ More Complicated → longer delay between stimulus & response ​ Involves @ least 1 interneuron between sensory neuron & motor neuron ​ >1 muscle grp → eg withdrawal effects ​ Autonomic Nervous System (ANS) ○​ Involved in autonomic regulation of body functions ○​ Uses two motor neurons from CNS to effector (cardiac & smooth muscle, glands & fat cells) ​ Preganglionic neurons communicate w ganglionic neurons whose axons are called postganglionic fibers ○​ Two divisions of ANS ​ Sympathetic division ​ Preganglionic fibers leave thoracic & lumbar spinal segments ​ Ganglia located near spinal cord ​ Short preganglionic fibers ​ Long postganglionic fibers  ​ Parasympathetic division ​ Preganglionic fibres originate in brain stem & sacral spinal region ​ Ganglia located near/ within target organs ​ Long preganglionic fibers ​ Short postganglionic fibers ​ Neurotransmitters at specific synapses ○​ All preganglionic fibers ​ Are cholinergic & release acetylcholine (ACh) ​ Are excitatory ○​ Postganglionic parasympathetic fibers ​ Are cholinergic ​ Effects are excitatory/ inhibitory depending on target cell receptor ○​ Most postganglionic sympathetic fibers ​ Are adrenergic & release norepinephrine ​ Usually excitatory ​ Sympathetic division ○​ Sympathetic chain ​ Arises from spinal segments T1-L2 ​ Preganglionic fibers enter sympathetic chain ganglia just outside spinal column ○​ The adrenal medullae ​ Centre of adrenal glands ​ Innervated by preganglionic fibers ​ Modified sympathetic ganglia (neurons) ○​ Secretes norepinephrine (NE) & epinephrine into capillaries, func like endocrine gland ​ Effect nearly identical to that of sympathetic postganglionic stimulation of adrenergic synapses ○​ Sympathetic division functions ​ Called “fight or flight” division ​ Effects: ​ Increase in alertness, metabolic rate, sweating, HR, blood flow to skeletal muscles ​ Dilates respiratory bronchioles & pupils ​ Blood flow to digestive organs decreased ​ E & NE from adrenal medullae support & prolong effect ​ Parasympathetic division ○​ Called rest & digest division ○​ Less divergence than in sympathetic division, effects more localised ○​ Effects:​ ​ Constrict pupils, increases digestive secretions, increases digestive tract smooth muscle activity ​ Stimulates urination & defecation ​ Constricts bronchioles, decreases HR ​ Dual innervation ○​ Refers to both divisions affecting same organs ○​ Mostly have antagonistic effects ○​ Some organs are innervated by only one division ​ Ascending pathways (sensory) ○​ Usually involves 3 sensory neurons: 1st, 2nd & 3rd order neurons ​ 1st order neurons: ​ Cell body at dorsal root ganglion of spinal cord ​ Axon projects to 2nd order neuron ​ 2nd order neurons: ​ Cell body @ brainstem or spinal cord ​ 3rd order neurons: ​ Cell body at thalamus ​ Projects to sensory cortex ○​ Posterior columns ​ Carries fine touch, pressure, vibration, proprioception to primary sensory cortex ○​ Spinothalamic pathways ​ Carries crude touch, pressure, pain, temperature to primary sensory cortex ○​ Spinocerebellar pathways ​ Carries proprioceptive info about position of skeletal muscles, tendons, joints ​ Involves only 2 sensory neurons, 2nd neuron goes to cerebellum instead of thalamus ​ Descending pathways (motor) ○​ Convey motor commands from CNS to peripheral effectors ○​ Distributed by: ​ Somatic nervous system ​ To skeletal muscles ​ Involves 2 neurons ○​ Upper motor neuron (LMN) ​ Located entirely in CNS ​ Synapses with LMN ○​ Lower motor neuron (LMN) ​ Cell body is in CNS; axon is in PNS ​ Controls skeletal muscles ​ Autonomic nervous system ​ Cardiac & smooth muscles, glands ​ Crossing over (decussate) ​ LMN →exits from spinal cord to reach skeletal muscles ​ All axons of corticospinal tract cross over to opposite side of spinal cord  ​ Result → left side controlled by right cerebral hemisphere & vice versa ○​ Pyramidal (corticospinal) pathways ​ Provide conscious, voluntary control of skeletal muscles ​ Responsible for initiating voluntary movements ​ UMN originates at motor cortex, axons descend down to brainstem & spinal cord, synapse on lower motor neuron nuclei @ anterior gray horn ○​ Extrapyramidal (medial & lateral pathways) ​ Provide subconscious involuntary control of posture, balance, muscle tone ​ Coordinate learned movement patterns ​ Consists of several tracts ​ UMN originates in several parts of brain eg basal nuclei, midbrain, cerebellum