Nervous System Lecture 5 PDF

NERVOUS SYSTEM HC1002 Anatomy Learning objectives 1. State the functions and structures of nervous system 2. Describe the functions and structures of a neuron 3. Identify the structures in the central nervous system (CNS) and state their functions respectively NERVOUS SYSTEM ◦ Functions...

NERVOUS SYSTEM HC1002 Anatomy Learning objectives 1. State the functions and structures of nervous system 2. Describe the functions and structures of a neuron 3. Identify the structures in the central nervous system (CNS) and state their functions respectively NERVOUS SYSTEM ◦ Functions 1. Monitor changes occurred both inside and outside the body through sensory receptors 2. Undergo integration ◦ Is a process of processing and interpreting the sensory input and give responses 3. Give a response by activating the effector organs ◦ Structures ◦ Mainly consist of two parts, 1. Central nervous system 2. Peripheral nervous system 1. Central nervous system (CNS) ◦ Consist of brain and the spinal cord ◦ Integrating and command center of the nervous system ◦ Receive incoming sensory signals, interpret these signals, and dictates motor responses 2. Peripheral nervous system (PNS) ◦ The part of the nervous system outside the CNS ◦ Consist of the nerves that extend from the brain and spinal cord ◦ Cranial nerves ◦ Carry signals to and from the brain ◦ Spinal nerves ◦ Carry signals to and from the spinal cord ◦ Ganglia ◦ Areas where the cell bodies of neurons are clustered NEURON ◦ Contain many billions of neurons (nerve cells) ◦ Are the basic structural units of the nervous system ◦ Have several functional characteristics 1. Responsible for conducting electrical signals from one part of the body to another 2. Have extreme longevity 3. Do not divide 4. Has high metabolic rate ◦ Structure ◦ Mainly consist of two parts 1. Cell body 2. Processes 1. Cell body ◦ The size vary widely in different neurons (from 5 – 140 m in diameter) ◦ Consist of a single nucleus surrounded by cytoplasm ◦ Mostly located within the CNS ◦ Clusters of cell bodies, called ganglia, lie along the nerves in the PNS 2. Processes ◦ Extend from the cell bodies of the neurons ◦ Divide into two types: dendrites and axons ◦ Dendrites ◦ Are processes that branch from the cell body ◦ Numerous dendrites can present in a neuron ◦ Act as receptive sites, providing a large surface area for receiving signals from other neurons ◦ Conduct electrical signals toward the cell body ◦ Axons ◦ Are thin processes of uniform diameter throughout their length ◦ Only one axon present in a neuron ◦ Transmit nerve impulses away from their cell body ◦ Myelin sheaths ◦ Are produced by oligodendrocytes in the CNS and Schwann cells in the PNS ◦ Are segmented structures composing of myelin ◦ Surround the axons of the body ◦ Functions: 1. Form an insulating layer that prevent the leakage of electrical current from the axon 2. Increase the speed of impulse conduction along the axon ◦ Synapses ◦ Are the sites at which neurons communicate ◦ Mostly communicate through chemical messengers ◦ Presynaptic neuron ◦ Refer to the neuron that conducts signals toward a synapse ◦ Postsynaptic neuron ◦ Refer to the neuron that transmit signals away from the synapse ◦ Functional classification of neurons ◦ can be classified functionally according to the direction the nerve impulse travels relative to the CNS 1. Sensory neurons ◦ Transmit impulses toward the CNS from sensory receptors in the PNS 2. Motor neurons ◦ Carry impulses away from the CNS to effector organs 3. Interneurons ◦ Lie between motor and sensory neurons ◦ Link together into chains that form complex neuronal pathways THE BRAIN ◦ Have distinct regions: gray matter and white matter ◦ Reflect the arrangement of their neurons 1. Gray matter ◦ Is a gray-colored zone ◦ Is the site where neuron cell bodies are clustered ◦ Found in the outer layer of the brain ◦ Located in the center of the spinal cord 2. White matter ◦ Consists of axons running between different parts of the CNS ◦ Its white color comes from the myelin sheaths around the axons ◦ Form the deep parts of the brain ◦ Form the superficial parts of the spinal cord ◦ Functions 1. Maintain the internal environment through control of the autonomic nervous system and the endocrine system 2. Perform high-level tasks which related to intelligence, consciousness, memory, sensory-motor integration, emotion, behavior, and socialization ◦ Consists of four parts 1. Brain stem 2. Cerebellum 3. Diencephalon 4. Cerebrum 1. Cerebrum ◦ Is made up of two cerebral hemispheres ◦ These hemispheres account for 83% of total brain mass ◦ Cerebral hemispheres are divided into five major lobes 1. Frontal lobe 2. Parietal lobe 3. Occipital lobe 4. Temporal lobe 5. Insula 1. Frontal lobe ◦ Located deep to the frontal bone ◦ Plan, initiate and enact motor movement ◦ Perform higher-order cognitive functions 2. Parietal lobe ◦ Deep to the parietal bones ◦ Conscious awareness of general somatic sensation ◦ Spacial awareness of objects, sounds and body parts ◦ Understanding of speech 3. Temporal lobe ◦ Lie on the lateral side of the hemisphere ◦ For hearing and smell ◦ Recognition of objects, words and faces ◦ Recognition of language and comprehension ◦ In emotional response and memory 4. Occipital lobe ◦ Lies deep to the occipital bone ◦ Form the most posterior portion of the cerebrum ◦ For vision 5. Insula ◦ Buried deep within the lateral sulcus and form part of its floor ◦ Covered by parts of the temporal, parietal, and frontal lobes ◦ For taste 2. Brain stem ◦ Consists of three regions 1. Medulla oblongata 2. Pons 3. Midbrain ◦ Each region is roughly an inch long ◦ Make up around 2.5% of total brain mass ◦ Functions 1. Acts as a passageway for all the fiber tracts running between the cerebrum and the spinal cord 2. Heavily involved with the innervation of the face and head 3. Produce the rigidly programmed, autonomic behaviors 4. Integrate auditory reflexes and visual reflexes 1. Medulla oblongata ◦ Is the lowest part of the brain stem ◦ Continuous posteriorly with the spinal cord ◦ Transmit signals between the spinal cord and the higher parts of the brain ◦ Contain the cardiac, respiratory, and vasomotor centers ◦ Cardiac center: adjust the force and rate of heartbeat ◦ Respiratory center: control the basic rhythm and rate of breathing ◦ Vasomotor center: regulate blood pressure by stimulating or inhibiting the contraction of smooth muscle in the walls of blood vessels 2. The pons ◦ Is a bulge located between the midbrain and the medulla oblongata ◦ Act as a bridge between various parts of the nervous system ◦ Many important nerves originate in the pons, eg facial nerve ◦ Involve in several autonomic functions ◦ Associated with the control of sleep cycles 3. Midbrain ◦ Is the topmost part of the brainstem ◦ The connection central between the brain and the spinal cord ◦ Serve important functions in motor movement, particularly movements of the eyes, and in auditory and visual processing 3. Cerebellum ◦ Make up 11% of the mass of the brain ◦ Located dorsal to the pons and medulla oblongata ◦ Smooths and coordinate body movements ◦ Help maintain posture and equilibrium 4. Diencephalon ◦ Form the central core of the forebrain and is surrounded by the cerebral hemispheres ◦ Consist of three paired structures 1. Thalamus 2. Hypothalamus 3. Epithalamus 1. Thalamus ◦ Is egg-shaped and is a paired structure ◦ Make up 80% of the diencephalon ◦ Relay information to the cerebral cortex ◦ Process the information as it pass through ◦ Organize and then either amplify or tone down the signals headed for the cerebral cortex 2. Hypothalamus ◦ Is the inferior portion of the diencephalon ◦ Is the main visceral control center of the body, regulating many activities of the visceral organs ◦ Control of the autonomic nervous system ◦ Regulation of body temperature ◦ Regulation of hunger and thirst sensations ◦ Regulation of sleep-awake cycles ◦ Control of the endocrine system ◦ Control of emotional responses ◦ Control of motivational behavior ◦ Formation of memory 3. Epithalamus ◦ Is the third and most dorsal part of the diencephalon ◦ Consist of pineal gland ◦ Under the influence of the hypothalamus ◦ Secrete the hormone, melatonin ◦ Signal the body to prepare for the nighttime stage of the sleep-awake cycle MENINGES ◦ Lie just external to the brain and spinal cord ◦ Are three connective tissue membranes 1. External layer: Dura mater 2. Middle layer: arachnoid mater 3. Inner layer: pia mater ◦ Functions ◦ Cover and protect the CNS ◦ Enclose and protect the blood vessels that supply the CNS ◦ Contain the cerebrospinal fluid CEREBROSPINAL FLUID ◦ Is a clear watery fluid that fills the subarachnoid space and the central hollow cavities of the brain and spinal cord ◦ Functions ◦ Provide a liquid medium that surround and give buoyancy to the central nervous system ◦ Prevent brain and spinal cord from being crushed under their own weight ◦ Resist compressive forces and cushions the brain and spinal cords from blows ◦ Helps to nourish the brain, to remove wastes produced by neurons, and to carry chemical signals between different parts of the CNS SPINAL CORD ◦ Run through the vertebral canal of the vertebral column ◦ Extend from the foramen magnum at the base of the skill’s occipital bone superiorly to the level of the first or second lumbar vertebra (L1 or L2) inferiorly ◦ Has 31 pairs of spinal nerves ◦ Named based on the vertebral locations in which they lie ◦ Divided into cervical (8), thoracic (12), lumbar (5), sacral (5), and coccygeal (1) groups ◦ Cervical and lumbar enlargements ◦ The regions showing obvious enlargements in the cervical and lumbar regions of the spinal cord ◦ Cauda equina ◦ The collection of nerve roots at the inferior end of the vertebral canal ◦ Functions 1. Involved in the sensory and motor innervation of the entire body inferior to the head 2. Provide a two-way conduction pathway for signals between the body and the brain 3. Served as a major center for reflexes References Britannica. (n.d.). Medulla oblongata. Retrieved from https://www.britannica.com/science/hindbrain Britannica. (n.d.). Midbrain. Retrieved from https://www.britannica.com/science/midbrain Healthline. (2018). Pons. Retrieved from https://www.healthline.com/human-body- maps/pons#1 Marieb, E. N., Brady, P. M. & Mallatt, J. (2020). Human anatomy (9th ed.). New Jersey: Pearson Education.