BIOL 1800 Nervous System Lecture 2024 PDF

CC - The nervous tissue, part 1 Lecture 8: Nervous Tissue & the Nervous System BIOL 1800 Dr Marie Conway The 4 types of body tissues Cells are the building blocks in the body A tissue is a group of cells that carry out a specific function – cells are organised into 4 tissue typ...

CC - The nervous tissue, part 1 Lecture 8: Nervous Tissue & the Nervous System BIOL 1800 Dr Marie Conway The 4 types of body tissues Cells are the building blocks in the body A tissue is a group of cells that carry out a specific function – cells are organised into 4 tissue types: 1. Epithelial Covers exposed surfaces, lines internal passageways, forms glands Fills internal spaces, provides structural support for other tissues, transports 2. Connective materials within the body, stores energy reserves Specialised for contraction, includes the skeletal muscles, muscle of the heart, 3. Muscular muscular walls of hollow organs Carries information from one part of the body to another in the form of 4. Nervous electrical impulses 1 and 2 are classified by morphology, 3 and 4 by function These tissues make up the organs and systems of the body Learning Outcomes for NS At the end of this week’s lectures you will be able to: List the parts of the Nervous system: CNS (brain and spinal cord) PNS (cranial and spinal nerves, sensory receptors) Explain the terms sensory, motor and integration as they apply to the nervous system Outline the structure of a nerve cell (neuron) and the function of each part of the neuron Explain the role of the glial cells Explain how neurons convey information in a reflex Nervous System Organs Organs of the Nervous System Brain and spinal cord Sensory receptors of sense organs (eyes, ears, etc.) Nerves connect nervous system with other systems (nerve is a bundle of axons). Spinal nerves and Cranial nerves Basic functions of nervous system Sensory function – senses certain changes (stimuli) both within (internal environment) and outside (external environment) the body Integrative function – analyses sensory information, stores some aspects, and makes decisions regarding appropriate behaviour Motor function – may respond to stimuli by initiating muscular contractions or glandular secretions The Nervous System Anatomical Divisions of the Nervous System Central nervous system (CNS) Brain and spinal cord Divided into grey and white matter Supported by glia, CT and blood vessels Peripheral nervous system (PNS) Cranial and spinal nerves Nerves can have both sensory and motor axons Nerves are supported by glia, CT and blood Includes somatic nervous system (SNS) and autonomic nervous system (ANS) The Central Nervous System (CNS) Consists of the spinal cord and brain Contains neural tissue (neurons and glia), connective tissues, and blood vessels Is protected by bone and meninges (CT) Functions of the CNS Are to process and coordinate: sensory data: from inside and outside body motor commands: control activities of peripheral organs (via muscles, glands) higher functions of brain: intelligence, memory, learning, emotion CNS – information processed at conscious and subconscious levels CNS – integrates physiology and psychology  E.g. in Thermoregulation CNS work example Blood temperature is the stimulus The hypothalamus can respond to the change in temperature (outside the set range) The hypothalamus in response turns on: Heat loosing or Heat gaining mechanisms Peripheral Nervous System All neural tissue outside the CNS Delivers sensory information to CNS; delivers motor commands from the CNS Bundles of axons (nerve fibres carry this information) Consists of 12 pair of cranial nerves and 31 pair of spinal nerves. The cranial nerves carry impulses between the brain, head and neck with only 1 exception (vagus nerve) The spinal nerves carry impulses between the spinal cord, the chest, abdomen and extremities Afferent division Brings information to the CNS Efferent division Carries motor commands to muscles and glands Somatic nervous system provides voluntary control Autonomic nervous system provides involuntary control Peripheral nervous system Somatic nervous system Autonomic nervous system Control skeletal muscle ANS automatically regulates contractions smooth muscle, cardiac muscle, Voluntary contraction – under glandular secretions, and adipose conscious control e.g. control over tissue at subconscious level arm to raise full glass of water to Parasympathetic and sympathetic your lips division  antagonistic effects Involuntary contractions – E.g. parasympathetic activity slows controlled at subconscious level e.g. the heart rate; - relax, digest, rest if you accidentally placing your Sympathetic activity accelerates the heart rate hand on hot stove you move it ② fight or flight reaction away immediately Automatic response is called a reflex  95% -brain + spinal cord Nervous tissue neurons- do not devide, the longest cell. limited ability to repair Neurons – basic functional unit of the nervous system Specialised for intercellular communication Nervous tissue also includes supporting cells called neuroglia, or glial cells Neuroglia have functions including: Survival and functioning of neurons Preserving the physical and biochemical structure of nervous tissue 70% of brain tumours are tumours of a glial cell 12 Nervous tissue ◦synapses 13 Neurons Four general regions: A large cell body Several short, branched dendrites Single, long axon Terminal branches of the axon called telodendria neurons can't be replaced when damaged - rapid change in neuro plasma from body to axon The cell body Large, round nucleus – prominent nucleolus Cytoplasm is the perikaryon - contain organels_-EF1, 3%273:É"ATP needs Cytoskeleton of the perikaryon contains neurofilaments and neurotubules Bundles or neurofilaments, called neurofibrils, extend into the dendrites and axon, providing internal support for them Dendrites Extend and branch out from the cell body Play key roles in intracellular communication Highly branched, some studded with projections called dendritic spines (0.5 to 1µm long) These participate in synapses In the CNS, a neuron receives information from other neurons primarily at the dendritic spines, which may represent 80-90 percent of the neuron’s total surface area Axons O Long cytoplasmic process capable of propagating an electrical impulse known as an action potential Axoplasm – cytoplasm of the axon contains neurofibrils, neurotubules, small vesicles, lysosomes, mitochondria, and various enzymes Axolemma – plasma membrane of the axon surrounds the axoplasm in the CNS, the axolemma may be exposed to interstitial fluid or it may be covered by the cellular processes of neuroglia Axon hillock – thickened region where the base (or initial segment) of the axon in a typical neuron joins the cell body Axons Axons create and pass electrical signals (AP) along their length. May be up to 1m long The end of the axon is called the synaptic terminal Chemicals are released from the synaptic terminal vessicles with chemicals, Nerves Communicate at a synapse communicate with posts. cell Chemical Junction gap called a synaptic cleft The synapse In the nervous system, messages move from one location to another in the form of action potentials along axons Transfer of message from one neuron to another takes place at a synapse  a specialised site where the neuron communicates with another cell Information passes from presynaptic neuron to postsynaptic neuron Synapses may also involve other types of postsynaptic cells e.g., the neuromuscular junction is a synapse in which the postsynaptic cell is a skeletal muscle fibre 2 types of synapses Electrical - direct physical contact between cell-rate Chemical - two cells, one sends, second reaives 19 The synapse Axon terminal of presynaptic cell releases chemicals called neurotransmitters into the synaptic cleft Neurotransmitters are contained in synaptic vesicles Synaptic cleft separates presynaptic membrane from postsynaptic membrane Each axon terminal contains mitochondria and vesicles filled with neurotransmitter molecules Chemical Junction gap called a synaptic cleft Telodendria Axon may branch along its length – producing side branches known as collaterals Collaterals enable a single neuron to communicate with several other cells The main axon trunk and any collaterals end in a series of find extensions called telodendria, or terminal branches Telodendria end at axon terminals, or synaptic terminals – role in communication with another cell Classification of Neurons by Structure based on dendrites in relation to cell body and axons Anaxonic neuron Bipolar neuron Unipolar neuron Multipolar neuron Anaxonic neurons Bipolar neurons have Unipolar neurons Multipolar neurons have more than two two processes have a single have more than two processes, and they separated by the cell elongated process, processes; there is a may all be dendrites; body. with the cell body single axon and axons are not obvious rare -sane organs-small located off to the side multiple dendrites - largest 30mn ◦ Longest - from tips of toes to most common spinal cord ◦ sensory neurons Classification of neurons by function Sensory neurons - unipolar neurons Also known as afferent neurons bodies Form afferent division of the PNS - celltcolated in pheripheral sensory ganglia bring nerve signals to the brain and spinal cord sensory receptors → brain Interneurons - connection in between bring nerve signals from one nerve cell to another within the brain and spinal cord  make connections between sensory and motor neurons Motor neurons - multi polar neurons bring nerve signals away from the brain and spinal cord reflex = brain → elector  The Nerve Cell (or Neuron) Structure Dendrites receive inputs Stimulus Stimulus Electrical signals travel out A chemical is released at the along the axon synapse  Just to know these 5? Neural activities make up the activity of movement signal 1. Resting potential - every cell hase, membrane potential of resting cell, when changed → starts the response is the signal movement 2. Graded potential - stimulus makes change in R. sp., signal is sent out, iffarge renough 3. Action potential - el- impuls, moves across axon to synapse 4. Synaptic activity - produce grated potential of posts. cell 5. Information processing - response of the posts. cell. Glia (neuroglia) - hold neurons in place and helps it perforce its function An axon with this insulation is called a myelinated axon and is much faster than an unmyelinated axon Many axons have an insulating coat around them This is formed by a glial cell This speeds the electrical conduction Glia are important in maintenance and repair Neuroglia – nervous tissue that support neurons Neuroglia: Separate and protect 2 types 4 types neurons Provide supportive framework for nervous tissue Act as phagocytes Help regulate the regulate ions,-- blood suply composition of interstitial fluid Neuroglia CNS 4 types of neuroglia Ependymal cell Microglial cell Oligodendrocyte - around 24 axons Astrocyte PNS 2 types of neuroglia Satellite cells - regulate interstatial fuid - same function as astrocytes? Schwann cells - myeline the axon - around just 1 axon Formation of myelin sheath in the PNS of Ranvier A myelinating Schwann cell myelinates only one axon (Figure 12-6a), (whereas an oligodendrocyte in the CNS may myelinate several axons) Non-myelinating Schwann cells can enclose segments of several unmyelinated axons A series of Schwann cells is required to enclose an axon along its entire length ( Figure 12-6b). 29 Formation of myelin sheath in the PNS Stages in the formation of a myelin sheath by a myelinating Schwann cell around the axon of a peripheral neuron Neural responses to injuries - it might not repair - bigger regeneration on PNS - eqtently degenerated - it works as before → synapse Neural reflexes Reflexes – quick, automatic responses triggered by specific stimuli; Regarded as fast, predictable, protective, automatic (subconscious) response to a stimulus - if the stimuli is the same, it will propably do the same response preserve homeostasis by making rapid adjustments in the function of organs or organ systems Spinal reflexes – controlled in the spinal cord, they function without any input from the brain E.g., a reflex controlled in the spinal cord makes you drop a frying pan you didn’t realise was sizzling hot Before the information reaches your brain and you become aware of the pain, you’ve already released the pan before you even realise, you've already done it Neural Reflexes - grasp, crawl - plantar reflex - from constant practise -driving... - sneezing, blushing, saliva production - knee or biceps reflex plantar reflex, patellar reflex Neural Reflexes Involves a circuit called a reflex arc This reflex arc includes: Sensory Receptor structure - object → pin.... Sensory nerve cell - sends signal to interneuron Interneuron(s) (in most cases) Motor nerve cell - sends signal to effector Effector- movement Spinal Cord Reflex Control Spinal cord transverse section formation of the action potential The monosynaptic reflex - delay between stimuli and the response Reflex Pathways CNS – brain and spinal cord Involve the central nervous system (brain and spinal cord) AND The peripheral nerves (cranial nerves, spinal nerves and sensory receptors) The sensory information is processed in the Central Nervous System (CNS) The CNS then directs the motor response → PNS Flow of information - se red light Example - driving a car - food go on the break Grey matter The CNS (brain and spinal cord) is divided into grey and white matter Grey matter of the brain and spinal cord is where nerve cell bodies are concentrated. Also the site of incoming signals (and therefore synapses) Grey because of cell body structures - cells which synthesise protein Decisions are made in the grey parts of the brain and spinal cord Spinal cord -31 segmens → 31 spinal nerve  Brain frontal section Grey matter is darker Grey matter is on the centre of the spinal cord Grey matter is mostly on the outside of brain tissue White matter of the brain and spinal cord White matter of the brain and spinal cord White matter colour is due to the is where bundles of axons are found glial cell membrane structure Glial cell White areas of the brain are the connections between one part of the brain and another White because of fatty tissue (myelin) in the glial cells that surround the axon Grey and White Matter Grey matter where information from one neuron is passed onto another neuron  this involves processing White matter where information is brought from one part of the CNS to another  this involves pathways called tracts Recap: Anatomical Divisions of the Nervous System Central nervous system (CNS) Brain and spinal cord Divided into grey and white matter Supported by glia, CT and blood vessels Peripheral nervous system (PNS) Cranial and spinal nerves Nerves can have both sensory and motor axons Nerves are supported by glia, CT and blood Nervous tissue 44