Nervous System Physiology Lecture 3 PDF

Nervous System Physiology Doctor Hussam Hadi Kadhum  CNS The Brain  The brain has four different regions: the cerebrum, diencephalon, brainstem, and cerebellum.  The cerebrum and diencephalon together constitute the fo...

Nervous System Physiology Doctor Hussam Hadi Kadhum  CNS The Brain  The brain has four different regions: the cerebrum, diencephalon, brainstem, and cerebellum.  The cerebrum and diencephalon together constitute the forebrain.  The brainstem consists of the midbrain, pons, and medulla oblongata.  The brain also contains four interconnected cavities, the cerebral ventricles, which are filled with fluid called cerebrospinal fluid (CSF) formed by specialized capillaries called choroid plexus that protect and cushioned the CNS.  Another protective device besides skull, meninges, and CSF which provide a physical protection, is the blood brain barrier (BBB) which is a structural arrangement of capillaries that selectively determines which substance can move from blood to into the brain. While substances such as oxygen and glucose are necessary to brain survival and consequently move freely across the BBB, other potential harmful substances, such as toxins, are prevented from crossing into the brain. Regions of brain  The CNS consist of Brain and Spinal cord The brain and spinal cord are enclosed by 3 membranes, collectively known as the meninges the outside membrane is the dura mater; the middle membrane is the arachnoid; the inside membrane is the pia mater.  Cerebrum the cerebrum is the larger component of the forebrain, governs all sensory and motor activity. This includes sensory perception, emotions, consciousness, memory, and voluntary movements. It is divided into the left and right hemispheres. The surface or cortex is arranged in bulging folds, each one called a gyrus, and furrows, each one called a sulcus.  the Cerebrum The cortex is also divided into 4 lobes that correspond to the overlying bones of the skull: the frontal lobe specializes in motor activity, personality, and speech; the parietal lobe is where language, temperature, pressure, touch are interpreted; the temporal lobe contains centers for hearing, smell, and language input; the occipital lobe specializes in vision.  The Cerebellum The cerebellum is the second largest part of the brain. It contains nerve fibers that connect it to every part of the central nervous system. It coordinates voluntary and involuntary patterns of movements. It also adjusts muscles to automatically maintain posture.  the Diencephalon The diencephalon refers to the thalamus and hypothalamus. The thalamus is the relay center for all sensory impulses except olfactory and motor areas of the cortex. The hypothalamus regulates behavior and emotional expression, body temperature, and many metabolic activities. Attached to the pituitary gland, it also controls hormonal secretions of this gland.  The Brainstem The brainstem consists of 3 structures: the gray matter of the midbrain control visual reflexes and sense of hearing. The white matter of the pons plays a role in regulating visceral control. The medulla oblongata connects the rest of the brain to the spinal cord. It regulates breathing, swallowing, coughing, sneezing, vomiting, heartbeat, and blood pressure. Spinal Cord  The spinal cord lies within the bony vertebral column.  It is a slender cylinder of soft tissue.  The 44 cm long spinal cord is shorter than the spinal column, so segments do not perfectly correspond to the vertebrae.  Spinal cord The central butterfly-shaped area of gray matter is composed of interneurons, the cell bodies and dendrites of efferent neurons, the entering axons of afferent neurons, and glial cells.  Spinal cord The regions of gray matter projecting toward the back of the body are called the dorsal horns, whereas those oriented toward the front are the ventral horns. The gray matter is surrounded by white matter, which consists of groups of myelinated axons. These groups of fiber tracts run longitudinally through the cord, some descending to relay information from the brain to the spinal cord, others ascending to transmit information to the brain.  Spinal cord  The spinal cord conducts impulses to and from the brain.  In most instances, sensory information traveling up the right side of the spinal cord crosses over to the left side of the brain, so the left hemisphere of the brain would, for example, interpret pain in the right hand. Conversely, motor impulses originating in the left brain cross to the right side of the spinal cord and initiate a response to the right side of the body. Because of this crossover effect, damage on one side of the brain typically causes manifestations itself on the opposite side of the body.  Peripheral nervous system  Neurons in the PNS transmit signals between the CNS and receptors and effectors in all other parts of the body.  The PNS has 43 pairs of nerves: 12 pairs of cranial nerves and 31 pairs of spinal nerves that connect with the spinal cord.  The 31 pairs of spinal nerves are designated by the vertebral levels from which they exit: cervical, thoracic, lumbar, sacral, and coccygeal.  PNS  The 12 pairs of peripheral nerves (cranial nerves) that connect and transmit messages directly to brain mediate many aspects of sensation and muscular activity in and around head and neck.  The 31 pairs of peripheral nerves (spinal nerves) connect and transmit messages directly to spinal cord.  The eight (8) pairs of cervical nerves innervate the neck, shoulders, arms, and hands.  The 12 pairs of thoracic nerves are associated with the chest and upper abdomen.  The five (5) pairs of lumbar nerves are associated with the lower abdomen, hips, and legs;  the five (5) pairs of sacral nerves are associated with the genitals and lower digestive tract.  A single pair of coccygeal nerves associated with the tailbone brings the total to 31 pairs.  PNS  All the spinal nerves contain both afferent and efferent fibers, whereas some of the cranial nerves contain only afferent fibers (the optic nerves from the eyes) or only efferent fibers (the hypoglossal nerve to muscles of the tongue).  The efferent division of the PNS is more complicated than the afferent?  being subdivided into a somatic nervous system and an autonomic nervous system.  The simplest distinction between the somatic and autonomic systems is that the neurons of the somatic division innervate skeletal muscle, whereas the autonomic neurons innervate smooth and cardiac muscle, glands, neurons in the gastrointestinal tract, and other tissues.  PNS The efferent somatic fibers that innervate skeletal muscles leave the CNS and pass without any synapses to skeletal muscle cells. The neurotransmitter that these neurons release is acetylcholine. Because activity in the somatic neurons leads to contraction of the innervated skeletal muscle cells, these neurons are called motor neurons. there are no somatic neurons that inhibit skeletal muscles. Muscle relaxation involves the inhibition of the motor neurons in the spinal cord.  Autonomic Nervous System  ANS innervate tissues other than skeletal muscles  Notice that in the GIT, A special case occurs where autonomic neurons innervate a nerve network in the wall of the intestinal tract. This network is called the enteric nervous system.  In contrast to the somatic nervous system, the ANS is made up of two neurons in series that connect the CNS and the effector cells.  Autonomic Nervous System  The first neuron has its cell body in the CNS. The synapse between the two neurons is outside the CNS in a cell cluster called an autonomic ganglion. The neurons passing between the CNS and the ganglia are called preganglionic neurons; those passing between the ganglia and the effector cells are postganglionic neurons. Autonomic nervous system… The autonomic nervous system is a part of the peripheral nervous system.. it controls the involuntary functions of the body such as sweating, gland secretions, blood pressure, and the heart. It is divided into the ‘sympathetic’ and ‘parasympathetic’ divisions. Autonomic nervous system… The sympathetic nervous system is responsible for the ‘flight or fight’ responses… increased alertness, metabolic rate, respiration, blood pressure, heart rate, and sweating AND a decrease in digestive and urinary function. The parasympathetic nervous system counteracts the responses of the sympathetic system… restoring homeostasis.  The neurons of the sympathetic and parasympathetic divisions leave the CNS at different levels—the sympathetic fibers from the thoracic (chest) and lumbar regions of the spinal cord, and the parasympathetic fibers from the brainstem and the sacral portion of the spinal cord. Therefore, the sympathetic division is also called the thoracolumbar division, and the parasympathetic division is called the craniosacral division.  The two divisions also differ in the location of ganglia. Most of the sympathetic ganglia lie close to the spinal cord and form the two chains of ganglia—one on each side of the cord known as the sympathetic trunks. In contrast, the parasympathetic ganglia lie within, or very close to, the organs that the postganglionic neurons innervate.  In the parasympathetic division, acetylcholine is the neurotransmitter between the postganglionic neuron and the effector cell. In the sympathetic division, norepinephrine is usually the transmitter between the postganglionic neuron and the effector cell. We say “usually” because a few sympathetic postganglionic endings release acetylcholine (e.g., sympathetic pathways that regulate sweating). A great majority of Ach receptors in the autonomic ganglia are nicotinic receptors. In contrast, the Ach receptors on cellular targets of postganglionic neurons are muscarinic receptors. The cholinergic receptors on skeletal muscle fibers, innervated by the somatic motor neurons, not autonomic neurons, are nicotinic receptor. The adrenergic receptors on most sympathetic postganglionic neurons are alpha ( α) and beta (β) receptors. THANK YOU