Nervous System PPT.pptx

Function: Detects impulses from the senses; control center. Major Organs: -Brain -Spinal cord -Senses -Nerves How is the nervous system organized? The nervous system is divided into Central nervous system (CNS), which consists of the brain and spinal cord Peripheral nervous system (PNS), which consi...

Function: Detects impulses from the senses; control center. Major Organs: -Brain -Spinal cord -Senses -Nerves How is the nervous system organized? The nervous system is divided into Central nervous system (CNS), which consists of the brain and spinal cord Peripheral nervous system (PNS), which consists of the other nerves Cranial nerves- originate in the brain Spinal nerves- originate in the spinal cord The peripheral nervous system is then further divided. Peripheral Nervous System (PNS), comprised of all nerves not in brain or spinal cord Sensory (Afferent) Division- sends impulses from the senses to the CNS Sympathetic Division- used in emergency situations (“fight or flight”) Parasympathetic Division- reduces sympathetic response and provides resting functions such as digestion and Motor (Efferent) Division- sends impulses from the CNS to the muscles and glands Autono mic Nervous Systeminvolunta ry muscle control Somati c Nervou s System voluntar y muscle control What are the major functions of the nervous system? The nervous system is the master control center for the body. It works with the endocrine system. To do this job, it uses: Sensory input- It detects changes (stimuli) inside and outside the body Integration- processing and interpreting the information Response- activation of muscles (motor output) or glands Summary The nervous system controls the body by receiving sensory input from the peripheral nervous system, integrating messages in the central nervous system, and responding through the peripheral nervous system. The PNS is divided into somatic (voluntary) and autonomic (involuntary) sections. What are the types of nerve cells? There are 2 major types of nerve cells: Neurons- conduct impulses around the body (make up only 10% of nerve cells) Neuroglia (“nerve-glue”)- support, insulate & protect neurons (90% of nerve cells) What is the structure of a neuron? Neurons have different structures, but all have a main cell body with processes extending outward. The cell body containscell body the nucleus, cytoplasm & organelles. processe s Processes are divided into: Dendrites- bring impulses towards the cell body Axons- send impulses away from the cell body At the end of the axons are axon terminals, which release neurotransmitters © Gnature with Gnat What are the types of neurons? single Neurons are classified by the process number of processes extending from the cell body. Unipolar neurons have one process bipolar unipolar Bipolar neurons have two processes multipol ar Multipolar neurons have Neurons can also be classified by their many processes function. Afferent neurons carry impulses toward the CNS. Efferent neurons carry impulses away from the CNS. Summary Neurons only make up 10% of the nervous system tissue, but they are essential cells for carrying impulses around the body. The impulses pass through the processes and into the cell body. Neurons can be classified by the number of processes they have or by their function. How is the myelin sheath created? Axons are wrapped in myelin, which is like a waxy insulation. To form the myelin, a Schwann cell (type of neuroglia) wraps itself around the axon, like a coil. The outer layers of the Schwann cell are called the neurilemma. Myelin helps the nerve impulses to travel more quickly. Collectively, the myelin wrappings are called the myelin sheath. Since the myelin sheath is formed by many Schwann cells, it has gaps What are the functions of neuroglia? Neuroglial cells are found in either the CNS or the PNS. Within the central nervous system: Astrocytes: Support & anchor neurons to surrounding capillaries Microglia: Provide immune response to central nervous system Ependymal cells: Secrete and circulate cerebrospinal fluid Oligodendrocytes: Provide myelin insulation to neurons in astrocyt es microgli a ependymal cells oligodendrocy tes What are the functions of neuroglia? Within the peripheral nervous system: Satellite cells: Support and anchor neurons in the peripheral nervous system Schwann cells: provide myelin insulation to neurons in the peripheral nervous system satellite cell Schwann cell Summary Neurons pass impulses to or from the CNS. The axon is covered by a myelin sheath, which is formed by Schwann cells. Neuroglia help to produce this insulation or support & anchor neurons, provide immune response or secrete cerebrospinal fluid. How is a nerve impulse passed along a neuron? A nerve impulse is an electrical signal that travels along the neuron. It arises from the movement of ions causing a change in electrical charges. At rest, a neuron’s intracellular space is negatively charged and the extracellular space is positively charged. This is called the resting potential. When the neuron is stimulated, either by the environment or another neuron, sodium rushes into the neuron and quickly reverses the charges (called depolarization). This depolarization is known as the action potential. This process quickly moves down the length of the neuron. As the impulse passes, potassium diffuses out of the neuron (repolarization). The sodium-potassium pump then restores the ion concentrations to normal and the resting potential returns. Watch the process at work by clicking on this video link. 1- Impulse arrives and threshold is met 2- Voltage-gated Na+ channels are opened and Na+ enters the cell 3- Voltage-gated K+ channels are opened and K+ leaves the cell; Na+ channels begin to rest 4- Voltage-gated K+5- Na+/K+ pump channels are still restores original levels of voltage in open; Na+ channels are in the cell resting state Direction of impulse Like flipping a light switch, a nerve impulse is an all-or-none response. Either the threshold is met and the impulse proceeds through the whole neuron, or it never starts at all. 3 2 1 4 5 What events occur at a synapse? Where 2 neurons meet is called a synapse. The 2 neurons do not touch. The space between them is called the synaptic cleft. As the impulse reaches the axon terminal, it can not cross the gap. The impulse stimulates vesicles to release neurotransmitters across the synaptic cleft. These neurotransmitters cause channels to open in the next neuron, continuing the action potential from one neuron to the next. Ca2+ channels open on presynaptic terminal Synaptic vesicles release neurotransmitter s Neurotransmitters bind to receptors on the postsynaptic neuron Action potential arrives at presynaptic terminal Na+ channels open on the postsynaptic neuron Impulse continues Summary When a neuron depolarizes due to a received stimulus, the action potential moves down the length of the axon. When the impulse reaches the axon terminals, it causes a release of neurotransmitters across the synaptic cleft to continue the impulse in the next neuron. What structures protect the central nervous system? The brain and spinal cord make up the Central Nervous System (CNS). These structures are protected by three layers of connective tissue called the meninges. Dura mater- thick, tough layer Arachnoid membrane- thin, cobweb-like layer Pia mater- thin layer containing lots of blood vessels Where is cerebrospinal fluid found & what is its function? Between the arachnoid layer and the pia mater is the cerebrospinal fluid (CSF). The cerebrospinal fluid protects the brain by preventing it from contacting the skull. It also maintains the blood-brain barrier, which controls homeostasis for the brain and prevents infection. The CSF is produced in spaces within the brain called ventricles. There are 4 ventricles: 2 lateral ventricles (right & left), third ventricle & fourth ventricle. The lateral ventricles are connected to the third ventricle by the thin interventricular foramen (foramen of Monro). Clusters of capillaries in the ventricles called choroid plexuses secrete CSF, it flows around the ventricles, then is absorbed by arachnoid granulations into the blood. CSF is constantly being produced, circulated and reabsorbed within these ventricles. Summary The brain is protected by several layers of connective tissue called meninges. Between these layers is the cerebrospinal fluid, which is produced by choroid plexuses in one of four ventricles and circulates around the brain, providing cushioning and preventing infection. What are the major regions of the cerebrum? The cerebrum is the largest part of the brain. It is divided into 2 hemispheres- right and left. These hemispheres are connected by a bundle of nerve fibers called the corpus callosum. The surface of the cerebrum is covered in ridges (gyri) and grooves (sulci). Deeper grooves called fissures divide portions of the brain. The brain has 3 major layers (from superficial to deep): 1. Cerebral cortex= “gray matter,” made of cell bodies & dendrites 2. Cerebral medulla= “white matter,” made of myelinated axons 3. Basal nuclei= islands of gray matter What are the functions of the lobes within the cerebrum? The cerebrum is divided into 4 lobes, based on their functions. They are named for the parts of the skull protecting them. Red- frontal Orange- Parietal Yellow- occipital Green- temporal *Blue section is the cerebellum, which is a separate portion of the brain. The frontal lobe controls: Voluntary movements (walking) Reasoning & decisionmaking Memory Ability to predict consequences of actions Planning Verbal communicationspecifically in the Broca’s area The parietal lobe is separated from the frontal lobe by the central sulcus. The parietal lobe controls: Sensations (pain, temperature, touch) Visual-spatial processing Body position The occipital lobe controls: Visual processingvision & memory of objects The temporal lobes are separated from the frontal lobe by the lateral sulcus. The temporal lobes control: Memory Comprehension & pronunciation of words Sensations of smell and sound Emotional association of memories Summary The cerebrum is the largest part of the brain. It contains 4 lobes. The frontal lobe controls movement and decision-making, the parietal lobe controls sensory information, the occipital lobe interprets visual cues, and the temporal lobes control memories and emotions. What structures are found in the diencephalon? Within the cerebrum, there is a small, nondescript region called the diencephalon. It contains the thalamus, the hypothalamus, and the pineal gland. The thalamus has 2 bulbshaped halves in the center of the brain. It relays sensory impulses to the cerebral cortex for processing and sorting. The pineal gland is posterior to the thalamus. (It will be discussed in the endocrine system). The tiny portion of the brain inferior to the thalamus is called the hypothalamus (“below thalamus”). It has several functions: Responsible for autonomic processes such as body temperature, metabolism, and blood volume Controls hormones released by pituitary gland Part of the limbic system, which regulates emotions and feelings of pleasure (thirst, hunger, sex, pain) What structures are found in the brain stem? The brain stem is located between the cerebrum and the spinal cord. It is broken into three regions: Midbrain Pons Medulla Oblongata The midbrain is also known as the mesencephalon Relays information to cerebrum Controls body movements and posture “Pons”= “bridge” Almost completely made of white matter that links the cerebral cortex and the cerebellum Carries information from one side of the brain to the other Central control of breathing The medulla oblongata is located just above the spinal cord. Transmits impulses between the spinal cord and the brain. Controls blood pressure, heart rate, swallowing, and coughing. Summary The diencephalon is surrounded by the cerebrum and contains 3 regions which relay sensory impulses, regulate the secretion of hormones, and control emotions like pleasure and pain. The brain stem also has 3 regions which relay information to the cerebrum and control autonomic processes like breathing and heart rate. What is the function of the cerebellum? The cerebellum, found near the back of the skull, is the second largest part of brain. It is responsible for coordinating the movements directed by the cerebrum so they are graceful and efficient (involuntary). After practicing a new sport or movement, the cerebellum also What is the structure and function of the spinal cord? The spinal cord extends from the medulla oblongata to the lumbar vertebrae. Like the brain, it is covered by meninges for protection. The spinal cord relays impulses between the peripheral nervous system and the brain A cross-section of the spinal cord has a “butterfly” of gray matter surrounded by white matter. The dorsal horns receive impulses from afferent nerves, then pass the impulses through the ventral horns to the efferent nerves. The dorsal and ventral roots contain the nerve fibers and join together to form a 2directional spinal nerve. How does a reflex arc travel? Preprogrammed responses are called reflexes and the pathway they travel is a reflex arc. A reflex arc involves: 1. 2. 3. 4. 5. A receptor Sensory neurons Integration Motor neurons An effector Reflexes can be somatic (involving skeletal muscles) or autonomic (involving smooth muscles). What type of reflex is this- somatic or autonomic? Summary The cerebellum coordinates movements so they are smooth and graceful. Extending from the brain is the spinal cord, which is made of gray and white matter. Impulses travel to the spinal cord through sensory neurons and return through motor neurons. This pathway is called a reflex arc.