Biology General Nervous System PDF

# BP201T. Human Anatomy And Physiology-II ## Unit-I: - Nervous System Represented By, Mr. Audumbar Mali, (Asst. Prof.) Sahyadri College of Pharmacy Methwade ## What is the nervous system? The nervous system is a highly complex part of the body that coordinates its actions and sensory information...

# BP201T. Human Anatomy And Physiology-II ## Unit-I: - Nervous System Represented By, Mr. Audumbar Mali, (Asst. Prof.) Sahyadri College of Pharmacy Methwade ## What is the nervous system? The nervous system is a highly complex part of the body that coordinates its actions and sensory information by transmitting signals to and from different parts of its body. The nervous system detects environmental changes that impact the body. ### The nervous system consists of two divisions: - the central nervous system containing the brain and spinal cord, - the peripheral nervous system which is a network of nerves and neural tissues branching out throughout the body. ## The Nervous System is divided into - Central nervous system (CNS) - receives and processes information; initiates action - **Brain** - receives and processes sensory information; initiates responses; stores memories; generates thoughts and emotions - **Spinal cord** - conducts signals to and from the brain; controls reflex activities - Peripheral nervous system (PNS) - transmits signals between the CNS and the rest of the body - **Motor neurons** - carry signals from the CNS that control the activities of muscles and glands - **Sensory neurons** - carry signals to the CNS from sensory organs **Motor nerves** that makeup - Somatic nervous system - controls voluntary movements by activating skeletal muscles - Autonomic nervous system - controls involuntary responses by influencing organs, glands, and smooth muscle - **Sympathetic division** - prepares the body for stressful or energetic activity; "fight or flight" - **Parasympathetic division** - dominates during times of "rest and rumination"; directs maintenance activities **Which consists of** - Sensory nerves ## Organization of the Nervous System ## Types of neurons... Neurons are the nerve cells, the structural and functional units of the nervous system. They conduct impulses that enable the body to interact with its internal and external environments. There are various types of neurons. The tissues that support the nerve cells is called neuroglia. ## Cells of the Nervous System * **Neurons** - Consist of three parts: * Cell body of neuron - main part * Dendrites - branching projections that conduct impulses to cell body of neuron * Axon - elongated projection that conducts impulses away from cell body of neuron ## Types of neurons - **The motor neurons** usually have one axon and several dendrites. The axon is covered with a insulating fatty layer called a myelin sheath, and transmits signals a long distance from the neuron to the area to be activated. Dendrites are short and unsheathed. Motor neurons cause muscle contractions and control secretions from glands and organs... controlling body functions. - **A diagram of a neuron is shown.** It includes: - Cell body - Nucleus - Dendrite - Myelin Sheath - Axon - Axon Terminals - Node of Ranvier - **Sensory neurons** do not have true dendrites. They are attached to sensory receptors and transmit impulses to the central nervous system, which then stimulate the interneurons, and then motor neurons. - **A diagram of a sensory neuron connected to the central nervous system (CNS) is shown.** It includes: - Cell body - Nucleus - Dendrite or peripheral process - Axon or central process - **Interneurons** are located entirely within the central nervous system. They intercept the impulses from the sensory neurons and transmit the signals to the motor neurons. ## Neuroglia (Glia) Support cells, bringing the cells of nervous tissue together structurally and functionally. Three main types of connective tissue cells of the CNS :- - **Astrocytes** - star-shaped cells that anchor small blood vessels to neurons - **Microglia** - small cells that move in inflamed brain tissue carrying on phagocytosis. - **Oligodendrocytes** - form myelin sheaths on axons in the CNS (Schwann cells form myelin sheaths in PNS only) **A diagram of a neuron with its associated neuroglia is shown.** It includes: - **Astrocytes** - **Microglia** - **Oligodendrocytes** - **Nerve fiber** - **Myelin sheath** ## Nerve fibers... - Schwann cells (i.e. cell around an axon of the peripheral nervous system to form the myelin sheath) - Myelin sheath, a fatty layer of insulation on some nerve fibers - The axon that transmits the message - There are no Schwann cells on nerve fibers in the central nervous system, therefore damage to those nerve fibers is not reversible. A bundle of nerve fibers is simply called 'a nerve'. AFFERENT nerves conduct impulses to the central nervous system; EFFERENT nerves conduct impulses to the muscles, organs, and glands. ## Synapses... - Definition – the place where impulses are transmitted from one neuron to another (the postsynaptic neuron) - Synapse made of three structures – synaptic knob, synaptic cleft, and plasma membrane conduction by the membrane - **A diagram of a synapse is shown.** It includes: - Cytoplasm of axon fiber - Synaptic cleft - Plasma membrane of postsynaptic neuron - Plasma membrane of Presynaptic neuron - Vesicles containing neurotransmitter molecules - Neurotransmitter molecules ## Neurotransmitters bind to specific receptor molecules in the membrane of a postsynaptic neuron, opening ion channels and thereby stimulating impulse. ## Some Neurotransmitters | Neurotransmitter | Location | Some Functions | |-------------------|---------------------------------|---------------------| | Acetylcholine | Neuron-to-muscle synapse | Activates muscles | | Dopamine | Mid-brain | Control of movement | | Epinephrine | Sympathetic system | Stress response | | Serotonin | Midbrain, pons ,medulla | Mood, sleep | | Endorphins | Brain, spine | Mood, pain reduction | | Nitric Oxide | Brain | Memory storage | ## Action Potential or Nerve Impulses:- - Definition – self-propagating wave of electrical disturbance that travels along the surface of a neuron membrane is called action potentials. ## Mechanism: - At rest, the neuron’s membrane is slightly positive on the outside—polarized—from a slight excess of Na+ on the outside. A stimulus triggers the opening of Na+ channels in the plasma membrane of the neuron ## Mechanism: - Inward movement of Na+ depolarizes the membrane by making the inside more positive than the outside at the stimulated point; this depolarization is a nerve impulse (action potential). The stimulated section of membrane immediately repolarizes, but by that time the depolarization has already triggered the next section of membrane to depolarize, thus propagating a wave of electrical disturbances (depolarizations) all the way down the membrane. ## Central Nervous System The central nervous system (CNS) controls most functions of the body and mind. It consists of two parts: the brain and the spinal cord. The brain is the center of our thoughts, the interpreter of our external environment, and the origin of control over body movement. ### Divisions of the brain :- - **Brain stem:-** Consists of three parts, named in ascending order: medulla oblongata, pons (lies between the medulla oblongata and the midbrain), and midbrain - **Structure** -white matter with bits of gray matter scattered through it ### Meninges: - - **Definition: -** Meninges (singular is meninx) is the collective term for the three membranes covering the brain and spinal cord. The meninges are composed of the dura mater (outer), the arachnoid (middle), and the pia mater (inner). In common usage, the membranes are often referred to as simply the dura, pia, and arachnoid. - **Dura** is the Latin word for hard, while **pia** in Latin means soft. The dura mater was so-named because of its tough, fibrous consistency. The pia mater is thinner and more delicate than the dura mater, and is in direct contact with the neural tissue of the brain and spinal cord. Along with the arachnoid layer and the cerebrospinal fluid (CSF), the dura and pia membranes help cushion, protect, and nourish the brain and spinal cord. ## Gray and white matter of the central nervous system... The brain and spinal cord of the central nervous system receive impulses, process the information, and respond with the appropriate action. - **Gray matter** of the brain and spinal cord consists of unsheathed nerve fibers (cannot be regenerated if damaged) in the cortex or surface layer. The white matter makes up the internal structure, and consists of myelinated nerve fibers. ## Brain and spinal cord meninges... The meninges are the membranes covering the brain and spinal cord. The brain and spinal cord are enclosed by 3 membranes, collectively known as the meninges (meh NIN jeez): the outside membrane is the dura mater: The middle membrane is the arachnoid, the inside membrane is the pia mater. ## The Brain - **Cerebrum** - **Frontal lobe** - **Temporal lobe** - **Parietal lobe** - **Occipital lobe** - **Cerebellum** - **Pons** - **Brain stem** ## Parts of the brain...the cerebrum Taking up 7/8ths of the brain’s weight, the cerebrum 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 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. ## Parts of the brain...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. ## Parts of the brain...the diencephalon The diencephalon refers to the thalamus and hypothalamus. The thalamus is the relay center for all sensory impulses except olfactory (sense of smell) 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. ## Parts of the brain... 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 (internal organ) 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. ## The spinal cord... The spinal cord has 31 segments: 8 cervical segments that correspond to the C1-C8 vertebrae; 12 thoracic segments corresponding to the T1-T12 vertebrae; 5 lumbar segments corresponding to L1-L5 vertebrae, 5 sacral segments corresponding to S1-S5 vertebrae, and 1 coccygeal segment. The 44 cm long spinal cord is shorter than the spinal column, so segments do not perfectly correspond to the vertebrae. ## Structure - The spinal cord is protected by the vertebrae. - Gray matter contains cell bodies; white matter contains myelinated fibers. - PNS nerves extend outside of the vertebrae. ## The spinal cord... At each segment of the spinal cord, left and right pairs of sensory and motor nerves branch out and connect to the peripheral nervous system. Impulses travel back and forth to the brain and back to the muscles. ## Cerebrospinal fluid... A fluid is produced in the ventricles of the brain; it surrounds the brain and spinal cord. It is called cerebrospinal fluid, and it cushions (i.e. something providing support) the brain and cord from shocks that could cause injury. It is maintained at a level around 1/2 - 2/3 cup. ## CSF acts as a cushion or buffer, providing basic mechanical and immunological protection to the brain inside the skull. CSF also serves a vital function in the cerebral auto regulation of cerebral blood flow. Cerebrospinal fluid has three main functions: CSF protects brain and spinal cord from trauma. CSF supplies nutrients to nervous system tissue. CSF removes waste products from cerebral metabolism. ## Reflex Arcs or reflex activity: - Nerve impulses are conducted from receptors to effectors over neuron pathways or reflex arcs; conduction by a reflex arc results in a reflex (i.e. contraction by a muscle or secretion by a gland). The simplest reflex arcs are two-neuron arcs-consisting of sensory neurons synapse in the spinal cord with motor neurons; these-neuron arcs consist of sensory neurons synapsing in the spinal cord with interneurons that synapse with motor neurons. The simplest neural pathway is the reflex arc. This involves one or more sensory neurons, association neurons in the spine, and motor neurons, which carry out the reflex entirely before the brain is aware of the response. ## Reflex Arc (NOT TO SCALE) - **white matter** - **cerebro-spinal canal** - **grey matter** - **dorsal fissure** - **ventral fissure** - **dorsal root** - **ganglion** - **sensory nerve cell body** - **stimulus** - **sensory nerve fibre** - **pain receptor in skin** - **relay nerve fibre** - **motor nerve fibre** - **motor-end plate** - **muscle (effector)** ## References: - Human Anatomy and Physiology, By Dr. S. B. Bhise, Dr. A. V. Yadav. Nirali Prakashan, As per PCI Syllabus, Page No. 1.1-1.24. - Human Anatomy and Physiology-II, By Dr. Mahesh Prasad, Dr. Antesh Kumar Jha, Mr. Ritesh Kumar Srivastav, Nirali Prakashan, As per PCI Syllabus. ## Thank you