001 Introduction - Basic Neurophysiology and Anatomy PDF

NERVOUS SYSTEM (NS)  Nervous System (NS)  Functions 1- Sensory input – monitoring stimuli occurring inside & outside the body 2- Integration – interpretation of sensory input 3- Motor output – response to stimuli by activating effector organs  Organization of the Nervous Sy...

NERVOUS SYSTEM (NS)  Nervous System (NS)  Functions 1- Sensory input – monitoring stimuli occurring inside & outside the body 2- Integration – interpretation of sensory input 3- Motor output – response to stimuli by activating effector organs  Organization of the Nervous System a)Central nervous system (CNS) (Brain and spinal cord) – Integration and command center b)Peripheral nervous system (PNS) (Paired spinal and cranial nerves) – Carries messages to and from the spinal cord and brain a)Central Nervous System: Brain (intracranial part) Spinal part  1. Brain (intracranial part): a) Cerebrum b) Brain stem c) cerebellum a. cerebrum: It is formed of 2 cerebral hemispheres The surface of each hemisphere is divided into 4 lobes 1. Frontal 2. Parietal 3. Temporal 4. occipital  Cerebral Cortex Each half of cortex divided into four major lobes Occipital lobe - carries out initial processing of visual input Temporal lobe - initial reception of sound sensation, taste, smell Parietal lobe - somatosensory processing Frontal lobe responsible for Voluntary motor activity Speaking ability planning of thought At the base of each cerebral hemisphere, there are several groups of nuclei situated at various levels within the white matter, they form: - basal ganglia, - thalamus, - subthalamus and - hypothalamus  Brain component Cerebral cortex Cerebral cortex Basal nuclei (lateral to thalamus) Basal nuclei Thalamus (medial) Thalamus Hypothalamus Hypothalamus Cerebellum Cerebellum Midbrain Brain stem Brain stem Pons (midbrain, pons, and medulla) Medulla Spinal cord b. Brain stem: It is formed of : 1. Midbrain 2. Pons 3. Medulla It is connected to the cerebral hemispheres by 2 cerebral peduncles and to the cerebellum, on each side, by the superior , middle & inferior cerebellar peduncles. the motor nuclei of the cranial nerves are arranged in the brain stem as follows: Cr 3&4 in midbrain Cr 5,6,7 ,8 in pons Cr 9,10,11 & 12 in medulla  Name Rhyme On Old Olympus’s Towering Top, A Finn And German Viewed Some Hops Function Rhyme Some Say Marry Money, But My Brother Says Big Brains Matter More S: Sensory M: Motor B: Both sensory and motor c. Cerebellum: It lies behind the brain stem it is concerned with coordination of voluntary motor activity and maintenance of equilibrium.  2. Spinal part: 1. Spinal cord 2. Cauda equina 1.Spinal cord: It lies in the spinal canal and ends at the lower border of the first lumbar vertebra. The lower most 3 segments of the spinal cord (S3,4,5) are known anatomically as the conus medullaris while the above 4 segments (L4,5,S1,2) are known anatomically as the epiconus It is formed of gray matter (cells) surrounded by white matter  In transverse section the gray matter resembles the letter H (2 anterior and 2 posterior horns) The white matter contains ascending and descending nerve fibers arranged into tracts The important tracts are: 2. Cauda equina: It is the collection of the lumbosacral roots which fill the lower part of the spinal canal below the lower border of L1 vertebra. N.B. cauda equina consists of nerve roots while the conus and epiconus form part of the spinal cord Common Words Used in Neurophysiology and Clinical Neurology Hemiplegia – Paralysis (loss of power) of half side of the body Hemiparesis – Partial loss of power of half side of the body Paraplegia – Paralysis in both legs Paraparesis – Partial loss of power in both legs Quadriplegia – Paralysis in all four limbs Monoplegia – Paralysis in one limb  B. Peripheral Nervous System: Efferent Division 1- Motor (efferent) division transmits impulses from the CNS to effector organs. 2- Sensory (afferent) division transmits impulses from effector organs to CNS.   Motor - General somatic motor – signals contraction of skeletal muscles under our voluntary control Often called “voluntary nervous system” - Autonomic (Visceral motor) Regulates the contraction of smooth and cardiac muscle Makes up autonomic nervous system Controls function of visceral organs Often called “involuntary nervous system” Autonomic nervous system   Sensory General somatic senses – receptors are widely spread Touch Pain Vibration Pressure Temperature Proprioceptive senses – detect stretch in tendons and muscle Body sense – position and movement of body in space Special somatic senses Hearing Balance Vision Smell Visceral sensory General visceral senses – stretch, pain, temperature, nausea, and hunger Widely felt in digestive and urinary tracts, and reproductive organs Special visceral senses - taste Stretch reflex (Descending tracts)  Types of stretch reflex: 1-Dynamic stretch reflex: Sudden stretch of a muscle rapid and strong contraction to oppose the sudden stretch. When the stretch is ended, the muscle relaxes rapidly. Example: tendon jerks. 2-Static stretch reflex: Slow prolonged stretch of a muscle continuous muscle contraction which is maintained so long as the muscle is kept stretched. Example: muscle tone.  Types of stretch reflex: 1-Dynamic stretch reflex: Sudden stretch of a muscle rapid and strong contraction to oppose the sudden stretch. When the stretch is ended, the muscle relaxes rapidly. Example: tendon jerks. 2-Static stretch reflex: Slow prolonged stretch of a muscle continuous muscle contraction which is maintained so long as the muscle is kept stretched. Example: muscle tone.  II- Tendon jerks: (Dynamic stretch reflex) 1- Definition: Sudden brief tap over a tendon of any muscle results in a sudden contraction of the muscle and jerky movement of the limb. 3- Clinical examples: 1. Knee jerk/reflex (center L: 2, 3,4) 2. Ankle jerk (center S: 1, 2) 3. Biceps jerk (C: 5, 6) 4. Brachioradialis jerk (C: 5, 6) 5. Triceps jerk (C: 6, 7) 6. Jaw jerk (center in the pons- trigeminal nerve (cranial nerve V):  Light tap on the chin when the mouth is slightly opened contraction of the masseter muscle and closure of the mouth.  Activity of  motor neurons is controlled by: control by Supra spinal centers: A) Supra spinal facilitatory centers: 1-Bulbo-reticular facilitatory area: It is a wide area of reticular formation which extends from the medulla (through the brain stem) up to thalamus and hypothalamus. It is self-active; its activity is transmitted along reticulo-spinal tract. 2-Motor area 4: Its activity is transmitted through pyramidal tract to the opposite side of the body. 3-Neo cerebellum: It increases the activity of the  motor neurons of the same side indirectly through stimulation of the bulbo-reticular facilitatory area and area 4. 4-Vestibular nucleus: It is present in the medulla and increase activity of the  motor neuron directly through vestibule-spinal tract and indirectly through stimulation of the bulbo- reticular facilitatory area.  B) Supra-spinal inhibitory centers: 1- Bulbo-reticular inhibitory area: It is localized area of reticular formation present in the medulla only. Its activity is transmitted through the reticulo-spinal tract (mainly lateral). 2- Suppressor areas of the cerebral cortex (e.g.. area 4s, 2s, 8s, 19s, 24s). These areas inhibit the activity of the  motor neuron of the opposite side through its effects on the bulbo-reticular inhibitory area. 3- Anterior cerebellum: It inhibits the activity of the  motor neurons of the same side through its effect on the bulbo- reticular inhibitory areas. 4- Basal ganglia: It inhibits the activity of the  motor neurons of the opposite side through stimulation of the inhibitory areas and inhibition of the facilitatory areas.  Motor Pathways (Descending tracts)  Functions of pyramidal tract: 1. It initiates voluntary, fine, discrete (isolated) movement in the opposite side of the body. So, electrical stimulation of the finger area leads to contraction of a single muscle or a small group of muscles. 2. It facilitates stretch reflex and muscle tone of the opposite side of the body (one of the supra-spinal facilitatory centers). 3. It also facilitates spinal reflexes and spinal centers.  Functions of extra-pyramidal tracts: 1) Regulation of equilibrium and maintain posture: These tracts control MT to maintain normal posture and to control equilibrium e.g.:  On standing position, the MT ↑ in the antigravity muscles to maintain normal posture.  Change in the position leads to change in the distribution of the MT so as to maintain equilibrium e.g., if a person is pushed backwards the MT ↑in the abdominal ms. And ↓ in the back ms. If he is pushed forward the reverse occurs. 2) Fixation movements: These are involuntary movements which occur in the trunk and proximal parts of the limbs to help the fine voluntary movements of the distal parts e.g., during writing the trunk, shoulders and elbow are involuntary fixed so as the voluntary movements of the fingers can be done easily and accurately. 3) Associated movements: The voluntary movements are usually associated with certain involuntary movements e.g.: Swinging movements of the arms during walking. Emotional expression e.g., facial expression which reflects the emotional state of the person. 4) Coordination of movements: Coordination occurs by cerebellum through its connection with the extra-pyramidal tracts. By coordination, the complex movements can be performed easily.  Feature UMNL LMNL Sie of lesion Cerebral hemisphere, AHC, nerve roots, spinal nerve, cerebellum, brain stem, peripheral nerve, NMJ, muscle spinal cord Paralysis Spastic paralysis Flaccid Paralysis MT Hypertonia Hypotonia (spasticity or rigidity) Deep reflexes Hyperreflexia+ clonus Hyporeflexia Superficial reflexes X Lost X Lost or normal (depending on affected spinal nerve) Wasting Delayed disused wasting Early marked wasting Response to electrical √ Normal response X abnormal response stimulation (reaction of degeneration) Involuntary movement X Absent √ present Muscle weakness Quadriplegia, hemiplegia, Proximal as in myopathy paraplegia, diplegia or Distal as in neuropathy Sensory loss Cortical sensory loss Peripheral sensory loss (fine touch loss) (pain- crude touch-temp) NCS √ Normal NCS X Abnormal NCS  Sensory Pathways (Ascending tracts)  spinothalamic Pathway Modalities carried: - Pain & temp: lateral - Crude touch & light pressure : anterior Pathway: - First order neuron: Cell body in dorsal root ganglia DRG synapse in posterior grey horn - Second order neuron: Cell body in posterior gray horn( in grey matter of the spinal cord). Its axon decussates immediately then ascend to thalamus - Third order neuron: Cell body in thalamus ascend to somatosensory cortex N.B: In the brain stem, ventral and lateral Spino-thalamic tracts join to form the spinal lemniscus.  II) Posterior column Pathway 1- Gracile tract 2- cuneate tract  Posterior column Pathway Modalities carried: - fine touch, Vibration & Proprioception Pathway: - First order neuron: Cell body in dorsal root ganglia DRG ascend to Medulla Oblongata - Second order neuron: Cell body in gracile and cuneate nuclei in Medulla Oblongata, its axon decussates in medulla then ascend to thalamus - Third order neuron: Cell body in thalamus ascend to somatosensory cortex N.B: - Fine touch (or discriminative touch) is a sensory modality that allows a subject to sense and localize touch. The form of touch where localization is not possible is known as crude touch - Deep or proprioceptive sensations (sense of position, sense of movements, sense of deep pressure, sense of muscle stretch and muscle tension).  III) Spinocerebellar Pathway Modalities carried: - Proprioceptive signals from trunk and limbs (unconscious proprioception) Pathway: - First order neuron: Cell body in dorsal root ganglia DRG Second order neuron: Cell body in in posterior gray horn (all proprioceptive information arrives on ipsilateral side synapse to a Purkinje cell in the cerebellum)