Nervous System Physiology PSL-223 August 2023 PDF

The Nervous System Dr. Atiq Hassan  Nervous System The human nervous system is highly complex. The nervous system is the communication system of the body. Controls body functions and actions. Maintains physiological homeostasis. It is divided into the ce...

The Nervous System Dr. Atiq Hassan  Nervous System The human nervous system is highly complex. The nervous system is the communication system of the body. Controls body functions and actions. Maintains physiological homeostasis. It is divided into the central nervous system, consisting of the brain and spinal cord; The peripheral nervous system: consist of cranial and spinal nerve.  Neurons Neurons are the fundamental units of the brain and nervous system. Each neuron consists of a cell body, axon and ,dendrites. Neurons are commonly referred to as nerve cells. Neurons cannot divide, and for survival they need a continuous supply of oxygen and glucose. Neurons generate and transmit electrical impulses called action potentials. Cell bodies form the grey matter of the nervous system. Groups of cell bodies are called nuclei in the CNS and ganglia in the PNS. 0 Functional components of the nervous system  Components of the Nervous System Central Nervous System: Brain and Spinal Cord Peripheral Nervous System: consist of two functional parts. Sensory division Motor division Motor division: It has two Parts Somatic nervous system: Controls the voluntary movement of skeletal muscles Autonomic nervous system (ANS): controlling Involuntary movement of Cardiac muscles (heartbeat), smooth muscles and glandular activity. Sympathetic Parasympathetic  Central nervous system (CNS) The central nervous system consists of the brain and the spinal cord. These essential structures are both well protected from damage and injury. The brain is enclosed within the skull and the spinal cord by the vertebrae that form the spinal column. Membranous coverings known as the meninges provide further protection.  Central Nervous System (CNS) Dura Mater – a tough, fibrous membrane that lies immediately internal to the skull and encloses the brain and spinal cord. Arachnoid-this is a delicate layer and a thin, cellular membrane, resembling a spider web. Pia Mater – This is a thin, delicate and highly vascularized membrane. loose tissue that covers the brain and encases the blood vessels that supply the brain. The cerebrospinal fluid (CSF) lies in the space between the arachnoid and pia mater layers. Its main function is to act as a cushion, helping to diminish the transmission of shocking forces.  Ventricles of the brain The brain contains four irregular shaped cavities, or ventricles, containing cerebrospinal fluid (CSF). Right and left lateral ventricles. These cavities lie within the cerebral hemispheres. They communicate with the third ventricle by interventricular foramina. Third ventricle. is a cavity situated below the lateral ventricles and between the two parts of the thalamus. Fourth ventricle: is a diamond shaped cavity situated below the third ventricle, between the cerebellum and pons. Ventricles of the brain  Cerebrospinal fluid (CSF) CSF is a clear, slightly alkaline fluid secreted into each ventricle of the brain by choroid plexuses. It is secreted continuously at a rate of about 0.5 mL per minute, i.e. 720 mL per day. The volume remains fairly constant at about 150 ml. The volume of CSF is reduced due to brain enlargement in e.g. tumour and haemorrhage. The volume of CSF is increased in condition such as brain atrophy, and degeneration.  Parts of the Brain The major parts of the brain are the brain stem, diencephalon, cerebrum, and cerebellum THALAMUS amygdala hippocampus Relays messages pituitary CEREBELLUM Coordination and balance BRAINSTEM Heart rate and breathing  Central Nervous System Cerebrum – it is the largest part of the brain distinguished by the folds or convolutions of much of its surface. The longitudinal cerebral fissure (deep cleft) divide it into right and left cerebral hemispheres. The hemispheres are connected by a mass of white matter (nerve fibres) called the corpus callosum. Each hemisphere of the cerebrum is divided into lobes four paired lobes – frontal, parietal, occipital, and temporal. Memory and conscious thought, speech, motor and sensory functions are controlled by the cerebrum.  THE CEREBRUM The cerebrum is the largest part of the brain. The surface layer, the cerebral cortex, is 2-4 mm thick and is composed of gray matter. The cortex contains billions of neurons. The cortex contains gyri (convolutions), deep grooves called fissures, and shallower sulci. Beneath the cortex lies the cerebral white matter, tracts that connect parts of the brain with itself and other parts of the nervous system. The cerebrum is nearly separated into right and left halves, called hemispheres, by the longitudinal fissure. Internally it remains connected by the corpus callosum, a bundle of transverse white fibers. Principles of Human Anatomy and Physiology, 11e 0 Cerebrum  Diencephalon This connects the cerebrum and the midbrain. It consists of several structures situated around the third ventricle. it is consist of the thalamus and hypothalamus,  Thalamus This consists of two masses of grey and white matter situated within the cerebral hemispheres just below the corpus callosum. It receives the sensory information from skin and viscera (organ) about touch, pain and temperature, and input from the special sense organs. The thalamus relays and redistributes information from most parts of the brain to the cerebral cortex. 0  Hypothalamus It is a small but important structure and consists of a number of nuclei. It is situated below and in front of the thalamus, immediately above the pituitary gland. It is linked to the posterior lobe of the pituitary gland by nerve fibres and to the anterior lobe by a complex system of blood vessels. It controls the output of hormones from both lobes of the pituitary gland. the autonomic nervous system appetite and satiety thirst and water balance body temperature emotional reactions, e.g. pleasure, fear, rage sexual behaviour sleeping and waking cycles.  Brain stem Brain stem is consist of: Midbrain Pons Medulla Oblongata The midbrain: it is the area of the brain situated around the cerebral aqueduct between the cerebrum and the pons. It consists of nuclei and nerve which connect the cerebrum with lower parts of the brain and with the spinal cord. The midbrain helps us orient our eye and body movements to visual and auditory stimuli.  Pons The pons is situated in front of the cerebellum, below the midbrain and above the medulla oblongata. It consists of nerve fibres that form a bridge between the Medulla and rest of the brain including spinal cord. It involved in respiration, movement, sleeping, waking, and dreaming. 0  Medulla oblongata The medulla oblongata is the most interior region of the brain stem. It is extending from the pons above, it is continuous with the spinal cord below. It contains the vital centres: cardiovascular centre respiratory centre reflex centres of vomiting, coughing, sneezing and swallowing 0  Cerebellum Cerebellum- “Little brain” – attached to back surface of brain stem. It is ovoid in shape and has two hemispheres, separated by a narrow strip called the vermis. Grey matter forms the surface of the cerebellum, and the white matter lies deeply. The cerebellum controls the automatic regulation of coordination and movement, balance, and posture, as well as skilled movements.  Central Nervous System Spinal Cord – A continuation of the brain which provides pathways to and from the brain, to and from the body. The spinal cord is also surrounded, protected, and nourished by cerebrospinal fluid. The vertebrae also serve as a bony protection to the spinal cord. The spinal cord terminates with the cauda equina.  Peripheral Nervous System Nerves are either motor nerves or sensory nerves. Efferent or motor nerves innervate muscles and glands. In order to accomplish this, they conduct nerve impulses from the CNS to the muscles and glands. Afferent or sensory nerves send sensory information and nerve impulses from sensory receptors in the skin, muscles, and joints to the brain.  Peripheral Nervous System Cranial Nerves – 12 pairs of cranial nerves which are either sensory or motor nerves. 10 of these nerves originate at the brain stem. Cranial Nerve 1: Olfactory – smell Cranial Nerve 2: Optic – vision. Cranial Nerve 3,4&6: Oculomotor, trochlear, and abducens – motor nerves controlling movement of the eyes. Cranial Nerve 5: Trigeminal – sensation of the head, face, and movements of the jaw. Cranial Nerve 7: Facial – taste, facial movements, and secretions of tears and saliva.  Peripheral Nervous System Cranial Nerve 8: Acoustic – hearing and equilibrium. Cranial Nerve 9: Glossopharyngeal – taste, sensation and movement in the pharynx, and secretion of saliva. Cranial Nerve 10: Vagus – controls specific body functions such as your digestion, heart rate and immune system. Cranial Nerve 11: Spinal accessory – It provide motor functions to two muscles essential to neck and shoulder movement, the sternocleidomastoid (SCM) and the trapezius. Cranial Nerve 12: Hypoglossal – It supply the muscles of the tongue and hyoid bone and contribute to swallowing and speech.  Peripheral Nervous System Spinal Nerves – there are 31 pairs of spinal nerves branching off the spinal cord. 8 cervical 12 thoracic 5 lumbar 5 sacral 1 coccygeal  Spinal reflexes A reflex action is an involuntary and immediate motor response to a sensory stimulus. These consist of three elements: Sensory neurones Interneurons in the spinal cord Motor neurones Reflexes may be used as diagnostic tools to determine nervous system disorders. Reflex pathways consist of sensory fibers bringing impulses into the spinal cord and motor fibers capable of effecting a response, as well as all the interconnections between the two.  Reflexes Stretch reflex: Only two neurones are involved. The cell body of the lower motor neurone is stimulated directly by the sensory neurone. Results in the contraction of a muscle when it is stretched suddenly. Example: patellar tendon reflex Autonomic reflexes. The pupil of eye immediately constricts, in response to bright light, preventing retinal damage. 0 Reflexes 0  Injuries and Diseases of the Nervous System Cerebral Concussion: an agitation or shaking of the brain by either a direct or indirect blow. Paralysis: The inability to voluntarily move a muscle or limb. Paraplegia – paralysis of both lower extremities. Quadriplegia – paralysis of both upper and lower extremities. Cerebral Palsy: Developmental defects of motor areas of the brain because of trauma at birth.  Injuries and Diseases of the Nervous System Parkinson’s Disease: A progressive disorder of the CNS (usually in individuals over 60 years of age). Production of Dopamine neurotransmitters is decreases in Parkinson’s disease. Cerebrovascular Accident (stroke): Arteries that supply blood to the brain cause blood clots to develop, obstructing blood flow to the brain, precipitating a stroke.