BMS100_PHL1-05v1_Fall2022 (2).pdf

Clinical Physiology V Fundamental Physiologic Basis of the Neurologic Exam – part 1 Dr. Fast BMS 100 Week 5 The Neurologic System Divisions of the Nervous System Central, peripheral, enteric Major anatomic structures of the central and peripheral nervous system Basic Functional Anatomy of the Nervou...

Clinical Physiology V Fundamental Physiologic Basis of the Neurologic Exam – part 1 Dr. Fast BMS 100 Week 5 The Neurologic System Divisions of the Nervous System Central, peripheral, enteric Major anatomic structures of the central and peripheral nervous system Basic Functional Anatomy of the Nervous System Components of the motor system and their roles Components of the sensory system relevant to the motor system The Neurologic Physical Exam – Part 1 Reflexes Cerebellar signs Other signs that evaluate the motor system Nervous tissue - review 1. The peripheral nervous system detects a stimulus and relays it to the central nervous system (sensory) 2. The central nervous system (brain, spinal cord) integrates this information → a response 3. The response is carried to effectors (muscles, glands, blood vessels) via the peripheral nervous system (motor) Nervous tissue - review The cells of the nervous system include: Neurons – an excitable cell that: ▪ receives a stimulus from a neuron or a receptor dendrites ▪ integrates it (ranks it, compares it to other stimuli) Cell body, axon hillock ▪ Passes along another stimulus if it is adequately stimulated axon Nervous tissue - review Axons are carried in bundles ▪ Nerves in the peripheral system ▪ Tracts in the central nervous system Most neuronal cell bodies reside in the CNS, with a few exceptions: ▪ Dorsal root ganglia – neuronal cell bodies for the axons that bring most sensory information from the PNS to the CNS ▪ Autonomic ganglia – help regulate the activities of the autonomic nervous system ▪ Enteric ganglia – help regulate the activity of the gut Overview of the Nervous System The Central Nervous System Structures Brain Cerebrum Cortex Basal Ganglia Limbic structures Thalamus Hypothalamus Cerebellum Brainstem Midbrain Pons Medulla Functions – the Cerebrum Cerebral Cortex Responsible for most of our “higher functions” ▪ Formation, storage, retrieval of memory Together with the limbic structures ▪ Speech & language ▪ Abstract thinking, math, planning and executing plans Also responsible for “what we’re conscious of” ▪ Perception (i.e. what we consciously sense) ▪ Voluntary movements, both simple and complex Basic Functional Anatomy of the Cortex Frontal Lobe Simple movements – precentral gyrus Complex motor plans – anterior portions + precentral gyrus Motor aspects of speech – anterior and inferior to the precentral gyrus Planning, abstract thinking, social behaviour (executive functions) – distributed throughout frontal and parietal lobes Basic Functional Anatomy of the Cortex Parietal Lobe Perception of touch, temperature, vibration – postcentral gyrus Perception of “where our limbs are” (proprioception) – postcentral gyrus Memory, executive functions, abstract reasoning – distributed throughout the parietal lobe Basic Functional Anatomy of the Cortex Temporal Lobe Hearing Scent, taste Recognition of speech Memory ▪ In cooperation with the limbic structures below it Basic Functional Anatomy of the Cortex Occipital Lobe Vision Areas that relate visual stimuli to “actual things” – i.e. association cortex Memories related to what has been seen Memory and the Cerebrum General statements about memory: Memory formation requires attention and structures that “process” and form new memories Attention → prefrontal loge Memory “processors” → the structures of the limbic lobe below the temporal lobe ▪ Hippocampus, amygdala Memory “storage” → Memories tend to be stored in the cortex “close to” the sensation they’re associated with i.e. – memory of a voice or word is likely in or close to the temporal lobe The Cerebrum – the Basal Ganglia Structures that lie below the cortex, close to the middle of the parietal and temporal lobes Serve to refine and regulate behaviours or movements ▪ Movements to be “inhibited” → tics, unnecessary movements, non-speech vocalizations ▪ They allow or “encourage” intended movements Impaired in several diseases – when they lose function: ▪ ▪ ▪ ▪ Tremors, rigidity, difficulty initiating movements Random, purposeless movements Tics, vocal utterances Personality changes Deep Structures in the Cerebrum Basal ganglia: ▪ Striatum ▪ Globus pallidus ▪ Subthalamic nuclei Limbic structures ▪ Approximate location of the amygdala and hippocampus: The Thalamus and Hypothalamus Thalamus – major roles Relays information from sensory receptors in the peripheral nervous system to the cortex ▪ Joint/limb position and movement ▪ Pain, touch, temperature Relays information from brain areas to refine motor planning ▪ Cerebellum, basal ganglia Hypothalamus – major roles Controls much of the endocrine system, along with the pituitary gland Regulates temperature, activity of the autonomic nervous system, fluid balance Some thalamic nuclei modulate emotion and memory formation The Thalamus and Hypothalamus The Cerebellum About 10% of the mass of the brain ▪ Highly folded, complex structure General function: ▪ Compares information from the receptors that sense: Joint position and movement Gravity and equilibrium ▪ Uses this information to adjust movements that are formulated in the prefrontal cortex It very quickly “error-corrects” movements that are planned by comparing them to data from the receptors described above The Cerebellum The Brainstem Composed of the midbrain, pons, and medulla Many functions that will be explored next day ▪ Cranial nerve nuclei are found throughout the brainstem All of the pathways that bring sensory information into the brain (from the PNS) or send motor information out of the brain (to the PNS) pass through the brainstem ▪ We will discuss discrete structures and functions next week Central Nervous System – Spinal Cord Like the brain ▪ isolated from the peripheral nervous system and rest of the body by a set of membranes (meninges) ▪ bathed in unique extracellular fluid (cerebrospinal fluid) ▪ Neurons or axons do not usually regenerate after they have been damaged Regeneration is common after damage to axons in the PNS Different (simpler) structure than the brain ▪ Dorsal components tend to carry sensory information to the brain ▪ Ventral components tend to carry motor information away from the brain to effectors (muscles in particular) Functional Anatomy – Spinal Cord Gray matter (yellow-coloured in this picture): ▪ Mostly cell bodies mixed with unmyelinated or lightlymyelinated axons ▪ Divided into two horns Ventral horns – cell bodies of neurons that activate skeletal muscles Dorsal horns – cell bodies of neurons that relay and integrate sensory information White matter ▪ Divided into columns – these are myelinated axons, no cell bodies Functional Anatomy – Spinal Cord Gray matter (yellowcoloured in this picture): ▪ Mostly cell bodies mixed with unmyelinated or lightly-myelinated axons ▪ Divided into two horns White matter ▪ Divided into columns – these are myelinated axons, no cell bodies ▪ Dorsal, lateral, and ventral columns Functional Anatomy – Spinal Cord Gray matter ▪ Dorsal horn – cell bodies and axons that integrate and transmit sensory information to the brain Which sensations? ▪ Ventral horn – mostly cell bodies of neurons that control skeletal muscles Functional Anatomy – Spinal Cord White matter ▪ Dorsal columns – proprioception (joint/limb position), vibration sense, fast pain fibres – sensory to brain ▪ Anterior and lateral columns – pain, temperature, itch – sensory to pain ▪ Anterior columns – motor information to skeletal muscles General Motor Systems Corticospinal tract: ▪ Motor plan formed (prefrontal cortex) → ▪ Activation of neurons in the primary motor cortex (prefrontal lobe) → ▪ Axons travel through the brainstem (medullary pyramids) and cross over to the opposite side → ▪ Activation of primary motor neurons in the ventral horn that stimulate skeletal muscle contraction OR ▪ Activation of motor neurons in the ventral horn that modify reflexes Lateral corticospinal tract – fine movements of extremities Anterior corticospinal tract – movements of the trunk Corticospinal tract – simplified Synapses are not shown Note the location of the ascending, sensory tracts as well It’s estimated that up to 90% of corticospinal output is to “shut down” reflexes that would oppose voluntary movements General Motor Systems Cerebellar modification of motor plans: cerebellum integrates information from proprioceptors (spinocerebellar tract) and the inner ear (vestibulocerebellar tract) ▪ Keeps the cerebellum “up-to-date” on the actual position of the body in general and specific joints compares this information with information from the motor “plan” generated by the frontal lobe ▪ relayed through the pons cerebellum “adjusts” the motor plan by communicating (via the thalamus) with the frontal lobe and refining the movements relayed by the corticospinal tract Sensory Pathways and the Motor System The motor system depends heavily on input from receptors about the position of a joint, tension across a joint, and tension in a skeletal muscle ▪ Together, these are known as proprioceptors Proprioceptors inform the cortex, the cerebellum and neurons in the spinal cord about the actual position of the body ▪ Dorsal column-medial lemniscal system proprioceptor → dorsal horn → dorsal column → thalamus → post-central gyrus of the parietal lobe ▪ Spinocerebellar system propriceptor → dorsal horn → dorso-lateral columns → cerebellum Reflexes A motor reflex is a fast, involuntary sequence of muscular movements that: ▪ do not need higher brain centres – brainstem or spinal cord circuits are adequate ▪ are simple – usually only a connections between groups of neurons are needed ▪ have a protective or stabilizing function – they help you pull away from a painful stimulus or help you stand ▪ need to be inhibited in order to perform purposeful, complex movements The inhibition often comes from higher brain centres Muscle spindle = a proprioceptor that senses muscle stretch As the muscle is stretched: ▪ activates the muscle to contract against the stretch by stimulating the motor neuron in the ventral horn ▪ inhibits the antagonist muscle Stretch caused by hitting the tendon with a reflex hammer Reflexes – the stretch reflex Types of reflexes Stretch reflex – helps to maintain posture Tendon reflex ▪ When a tendon is stretched, the antagonist muscle contracts and the agonist relaxes ▪ Thought to help prevent tearing the tendon during excessive force generation Withdrawal reflex ▪ In response to a painful stimulus, muscles of flexion are activated to withdraw a limb Plantar reflex ▪ In response to an irritating stimulus, the foot plantar flexes (foot flexes “down”) and the toes curl The Neurological Physical Exam Deep Tendon Reflexes (DTRs) ▪ These are simple stretch reflexes activated by striking the tendon with a reflex hammer → contraction of the agonist muscle ▪ Examples – patellar reflex, triceps reflex ▪ Causes of absent DTRs: normal variation (some people are really difficult to get reflexes from) damage to sensory or motor nerves innervating the muscle being tested ▪ Causes of excessive DTRs loss of inhibition of reflexes from higher brain centres – usually the corticospinal tract (so damage to the corticospinal tract) Reflexes are easier to interpret as abnormal when they are asymmetrical – one side greater/less than the other side The Neurological Physical Exam Plantar reflex ▪ When the lateral side of the foot is stroked firmly, the foot should plantar flex (ankle moves foot downwards) and toes should curl ▪ This develops as we learn to walk – it depends on the corticospinal tract providing specific feedback to particular segments of the spinal cord (S1) ▪ If the foot dorsiflexes and the toes spread, this indicates that the corticospinal input to the lower limb is poor ▪ an “upgoing” plantar reflex is usually an abnormal finding Cerebellar Tests in the Neurological Exam Cerebellar tests include: ▪ rapid alternating movements (RAMS) ▪ point-to-point movements (i.e. patient touches his nose then rapidly touches your finger, and repeats) ▪ heel to shin movements ▪ Gait – how coordinated is the patient’s gait? All of these tests rely on the ability of the cerebellum to evaluate the body’s position and provide feedback to the rest of the motor system If the cerebellum has lost function, then these movements are often clumsy, uncoordinated, and slow Romberg sign This test is thought to evaluate the function of the dorsal columns ▪ Sensory input from proprioceptors to the cerebellum and the parietal cortex – key for joint and limb position sensing Patient stands with feet together and closes her eyes ▪ If the patient loses balance and starts to fall (support the patient!), indicates that the dorsal columns could be damaged visual input is no longer available to help the patient keep her balance Corticospinal tract test – pronator drift The brain structures in the corticospinal tract can be damaged in a wide variety of ways ▪ stroke, trauma, demyelinating disease, tumours ▪ structures include the precentral gyrus and prefrontal cortex Corticospinal tract damage often results in a pattern of loss of muscle strength – extensors and supinators of the arm are weaker than the pronators or flexors Patient stands with arms outstretched, palms up, hand open, eyes closed ▪ The arm “drifts” to a more pronated position, the hand closes, and the arm tends to descend