INTRODUCTION TO NEUROLOGY J M Stansbie Warwick Medical

INTRODUCTION TO NEUROLOGY J. M. Stansbie Warwick Medical School

Structural Units of the Nervous System • Neurone – an excitable cell specialised for the reception of a stimulus and the conduction of an impulse. Found in brain, spinal cord and ganglia. Communicate at synapses.

Structural Units of the Nervous System • Neurone – an excitable cell specialised for the reception of a stimulus and the conduction of an impulse. Found in brain, spinal cord and ganglia. Communicate at synapses. • Neuroglia – non-excitable cells in CNS. i) Astrocytes – provide anatomical and functional supporting framework for nerve cells and fibres. ii) Oligodendrocytes – form myelin sheaths of nerve axons. iii) Microglia – involved in inflammatory response. Derived from macrophages outside nervous system. iv) Ependyma – lines cavities in CNS. Involved in production and circulation of cerebrospinal fluid.

Structural Units of the Nervous System • Neurone – an excitable cell specialised for the reception of a stimulus and the conduction of an impulse. Found in brain, spinal cord and ganglia. Communicate at synapses. • Neuroglia – non-excitable cells in CNS. i) Astrocytes – provide anatomical and functional supporting framework for nerve cells and fibres. ii) Oligodendrocytes – form myelin sheaths of nerve axons. iii) Microglia – involved in inflammatory response. Derived from macrophages outside nervous system. iv) Ependyma – lines cavities in CNS. Involved in production and circulation of cerebrospinal fluid. • Schwann cells – peripheral nervous system equivalent of oligodendrocyte.

Peripheral nerve

Divisions of the Nervous System Central Peripheral Somatic Sensory Visceral Motor Sensory Motor Sympathetic Parasympathetic

Central and Peripheral Nervous Systems

CNS - Brain

CNS - Brain

CNS - Brain

CNS – Spinal cord

CNS – Meninges

PNS - Cranial Nerves Rostral; Cranial; Anterior Caudal; Posterior

PNS – Spinal nerves (1)

PNS – Spinal nerves (2) Dermatome – area of skin supplied by a single spinal nerve. Myotome – group of muscles supplied by a single spinal nerve.

Divisions of the Nervous System Central Peripheral Somatic Sensory Visceral Motor Sensory Motor Sympathetic Parasympathetic

Somatic Sensory System modalities General Pain Temperature Touch(crude; two point) Pressure Proprioception Special Olfaction (I) Vision (II) Taste (V, VII, IX) Hearing (VIII) Balance (VIII)

Somatic Motor System • Cerebral cortex; limbic system; basal ganglia – planning, programming and initiation of movement. • Cerebellum - co-ordination; learning/memory. • Descending tracts (upper motorneurones) - influence reflexes and lower motorneurones. • Lower motorneurones - final common pathway. • Spinal cord – reflexes.

Motor Unit • This is the basis of movement. • It comprises a single alpha-motorneurone and all the muscle fibres supplied by it. • Each muscle contains thousands of motor units.

Muscle Contraction • Results from the synchronous action of multiple motor units. • Muscle power depends on the number of motor units recruited(active) at any one time. • Motor units rotate their activity over time. • Is facilitated by reflex inhibition of antagonists through reciprocal innervation.

Muscle Tone (1) • Is a state of partial contraction in resting muscle. • Is dependent on the stretch reflex involving muscle spindle receptors and alpha motorneurones. • Muscle spindles are rapidly responsive to the absolute length and rate of change of length of muscle and dynamically adjust their own muscle fibre length and tone as appropriate via reflexes involving gamma motorneurones. • The activity of gamma motorneurones, and therefore muscle tone, is influenced by the descending tracts.

Muscle Tone (2) • Golgi tendon organs are sensitive to tension and are involved in a reflex which protects muscle from damage due to excess tension but also provide the CNS with information which may influence voluntary muscle activity. • The assessment of clinical phenomena based on variations in muscle tone is an important component of the examination of the somatic motor system.

Visceral Sensory System modalities Pain Stretch/pressure Chemical Osmotic pressure Arterial pressure

Visceral Motor System Sympathetic • • • Prepares body for emergency Increases heart rate Constricts arterioles of gut and skin Dilates arterioles of muscle Increases blood pressure Dilates pupils Relaxes bronchial smooth muscle Closes sphincters Stimulates sweating Parasympathetic • • • Allows body to conserve energy Reduces heart rate Dilates arterioles of gut and skin Reduces blood pressure Constricts pupils Constricts bronchial smooth muscle Increases gut peristalsis Relaxes sphincters Stimulates glandular secretion

Visceral Motor System Sympathetic

Visceral Motor System Parasympathetic