ANIM 1005 Veterinary Anatomy and Physiology Lecture Notes PDF

2024-09-20 ANIM 1005 Veterinary Anatomy and Physiology Dr. Pauline Smith Contact: [email protected] Rm 00600 1 1  2024-0...

2024-09-20 ANIM 1005 Veterinary Anatomy and Physiology Dr. Pauline Smith Contact: [email protected] Rm 00600 1 1  2024-09-20 Outline for today’s class: ▪ Nervous system anatomy ▪ Cell types of the nervous system ▪ Parts of the Neuron ▪ The synapse Test # 3 Tuesday Oct 15th: Nervous System and Muscular Contraction 75 min (12:30-1:45), Format: true/False Multiple choice Short Answer 2 2  2024-09-20 Nervous System Nervous System: Functions: 1) coordinate and control body activity 2) detect and process internal and external information and formulate appropriate responses (to maintain homeostasis) Neuron: basic unit of the NS Nerves: one or more bundles neurons (impulse-carrying fibers) that connect the central nervous system (CNS) to other parts of the body 3 3  2024-09-20 Organization of Nervous System Anatomical Central nervous system (CNS) – Brain and spinal cord – Regenerative Capacity: axons do not effectively regenerate Peripheral nervous system (PNS) – Extends outward from the central axis toward the periphery of the body – Composed of 1) Cranial nerves originate directly from the brain 2) Spinal nerves emerge from the spinal cord – Regenerative Capacity: axons can slowly regrow and connect to their peripheral targets 4 4  2024-09-20 Organization of the Nervous System 5 5  2024-09-20 Central Nervous System (CNS) 6 6  2024-09-20 CNS (cont) 1) Brain: located in the cranium 2) Spinal Cord: protected by vertebrae intervertebral disks: layers of cartilage between the vertebrae that separate and cushion the vertebrae from each other Regenerative Capacity: axons of the CNS do not effectively regenerate 7 7  2024-09-20 Anatomical Organization of the CNS Brain: Regions: Telencephalon (Cerebrum); Diencephalon (thalamus, hypothalamus); Cerebellum; Brainstem (Midbrain, pons, medulla oblongata) Spinal cord 8 8  2024-09-20 CNS: Spinal Cord Anatomy Grey matter: Central portion containing neuronal cell bodies White matter: Outer portion containing neuronal axon tracts Protected within vertebral canal - sensory information motor information 9 9  2024-09-20 CNS: Meninges Meninges: 3 layers of connective tissue that surrounds the brain and spinal cord Dura mater: tough fibrous outer layer, fused to periosteum of cranial bones epidural: located above the dura mater Arachnoid: middle layer Pia mater: attached to the surface of the brain anchored by processes of astrocytes 10 10  2024-09-20 CNS: Meninges (cont) Contains the CSF Brain Spinal Cord 11 11  2024-09-20 Peripheral Nervous System 12 12  2024-09-20 Peripheral Nervous System (PNS) Extends outward from the central axis (brain and spinal cord) toward the periphery of the body Composed of: cranial nerves originate directly from the brain spinal nerves emerge from the spinal cord Regenerative Capacity: axons can slowly regrow and connect to their peripheral targets 13 13  2024-09-20 PNS: Cranial Nerves originate directly from the brain I II III IV V VI VII VIII IX XII X XI 14 14  2024-09-20 PNS: Spinal Nerves Originate from the spinal cord Carries motor, sensory, and autonomic signals between the spinal cord and the body - 38 pairs of spinal nerves in the cat, each roughly corresponding to a segment of the vertebral column (thorac/o) (lumbo/o) (sacr/o) (cervic/o) (coccyg/o) Coccygeal 15 15  2024-09-20 PNS: Spinal Nerves (cont) receives sensory input along sensory dorsal root axons from receptors in the skin, muscle, tendons, joints and visceral organs motor neurons exit to innervate skeletal muscle or toward smooth muscle 16 16  2024-09-20 PNS: Sensory and Motor Neurons Brings info to the CNS Sends info to the periphery 17 17  2024-09-20 PNS: Sensory and Motor Neurons (cont) The PNS consists of sensory neurons running from stimulus receptors that inform the CNS of the stimuli and motor neurons travelling from the CNS to the muscles and glands (effectors) that take action. (Visceral Afferent Neurons) (Somatic Afferent Neurons) (Visceral Motor Neurons) (Somatic Motor Neurons) 18 18  2024-09-20 PNS: Direction of Impulses Direction of Impulses (action potentials) Afferent nerves: conduct impulses toward CNS Also called sensory nerves: conduct sensations from sensory receptors in the skin and other locations in the body to the CNS Efferent nerves: conduct impulses away from CNS Also called motor nerves: cause skeletal muscle contraction and movement, gland secretion etc 19 19  2024-09-20 PNS: Direction of Impulses (cont) (sensory neuron) (motor neuron) 20 20  2024-09-20 Organization of the Nervous System 21 21  2024-09-20 PNS: Somatic vs Autonomic Nervous System Somatic Nervous System: actions under conscious (voluntary) control (conscious perception by the brain) → Somatic afferent and efferent neurons Autonomic Nervous System: controls & coordinates automatic (involuntary) functions including life support functions (no conscious perception by the brain) → Visceral afferent and efferent neurons 22 22  2024-09-20 PNS: Autonomic Nervous System Autonomic Nervous System (ANS): controls and coordinates automatic (involuntary) functions controls muscle (smooth and cardiac) and glands 3 divisions 1) parasympathetic: rest and digest Work together 2) sympathetic: fight or flight } to maintain homeostasis 3) enteric: in the GI tract Visceral afferent neurons: conduct impulses toward CNS from receptors in visceral organs of the chest, abdomen (include stretch receptors, chemoreceptors (CO2 or O2), olfactory epithelium, taste buds) Visceral efferent neurons: conduct impulses away from CNS to smooth muscle, cardiac muscle and some exocrine glands 23 23  2024-09-20 Functional Organization of the Nervous System 24 24  2024-09-20 Functional Organization of the Nervous System: another look 25 25  2024-09-20 CNS: Cerebral Spinal Fluid Cerebrospinal Fluid (CSF): - clear fluid that 1) nourishes 2) cools 3) cushions - produced by the choroid plexus - contains very few cells and little protein - absorbed into the venous circulation through the arachnoid villi into the dural sinus to mix with venous blood - replaced several times daily CSF tap 26 26  2024-09-20 Cerebrospinal Fluid (CSF) Produced by choroid plexus – Circulates – Contains very few cells and little protein – absorbed into the venous circulation through the arachnoid villi into the dural sinus to mix with venous blood – replaced several times daily 27 27  2024-09-20 Location of Ventricles (Lateral View) 28 28  2024-09-20 Roles of the CSF 1) Protection – Cushions the brain from blows to the head 2) Maintains consistent environment for neurons and glia – Composition of CSF is controlled and in equilibrium with extracellular fluid of the brain 3) Buoyancy – Immersion of brain in CSF ↓ pressure on base of brain 4) Excretion of waste products – 1-way flow of CSF to the blood removes potentially harmful substances from the brain 5) Endocrine medium for the brain – CSF transports hormones to other areas of the brain 29 29  2024-09-20 Circulation of CSF CSF is orange : common CSF sampling location 30 30  2024-09-20 CSF is Absorbed into Venous System CSF enters subarachnoid space, flows into the arachnoid villi which project into the sagital sinus. The CSF crosses into the venous sinus. CSF pressure is regulated by absorption rate. Obstruction of CSF absorption results in ↑ CSF pressure. ↑ pressure seen with brain Figure 15-4 tumors and meningitis 31 31  2024-09-20 Cerebrospinal Fluid: Tests Spinal Tap – common diagnostic procedure – pressure, cell count, biochemical composition Myelography – radiopaque dye into subarachnoid space to assess integrity of spinal canal 32 32  2024-09-20 Blood Brain Barrier (Anatomy) Protects neurons and glia: hormones, large molecules, charged molecules & circulating chemicals How do we know this barrier exists? Systemic dyes do not stain the brain! 33 33  2024-09-20 Circumventricular Organs Specialized areas of the brain that lack the normal blood brain barrier – Brain capillaries do not form tight junctions – Important to detect levels of circulating substances from the periphery 34 34  2024-09-20 Damage to the Blood Brain Barrier 1) Hypertension – high BP opens BBB by expanding vessels 2) Development – BBB not fully formed at birth 3) Hyperosmolarity – High concentration of solutes can open BBB 4) Infection – Exposure to infection agents can open BBB 5) Trauma, Ischemia, Inflammation, Pressure – Injury to brain can open BBB 35 35  2024-09-20 36 36  2024-09-20 Cell Types of the Nervous System Neurons and Neuroglia (Glia) 37 37  2024-09-20 Neuroglia (Glia) 2nd cell type in the NS (10-50x the number of neurons) do not conduct action potentials Structural and functional support to neurons Produce myelin sheaths Modulate growth of developing neurons Buffer ion and neurotransmitter concentrations Immune response of the nervous system Modulate effectiveness of neural communication by monitoring electrical activity of neurons 38 38  2024-09-20 Glial Cell Functions 39 39  2024-09-20 Neurons Basic functional unit of the nervous system Conduct action potentials (how neurons send messages - more to follow) Cannot reproduce but can regenerate cell processes if the cell body remains intact Complexity of the brain is due: 1) to large # of neurons (1012 neurons in the brain) 2) the interconnections of the neurons. 40 40  2024-09-20 Diverse Neuron Forms and Functions 41 41  2024-09-20 Parts of the Neuron (presynaptic terminal) Direction of Impulse (action potential) 42 42  2024-09-20 The Neuron: Anatomical Regions Dendrites: Carry impulses (information) toward the cell body Cell Body (soma): processes information and manufactures proteins for cell function Axons: integrates and carries information (via action potentials – more to follow) Presynaptic terminals: transmits information to adjacent cells Together, these regions: 1) collect information from the environment, 2) integrate that information, and 3) produce an output that can change the environment 43 43  2024-09-20 Dendrites ▪ Receive signals from neighboring neurons signals (neurotransmitters) from neighboring cells act on receptors on the dendrites multiple branchlike extensions from the cell body SYNAPSE (more to follow!) 44 44  2024-09-20 Cell Body (soma) ▪ process the information it receives and manufactures proteins for neuron function nucleus (contains DNA) free ribosomes (cytosolic protein assembly) rough endoplasmic reticulum (assembly of secretory and membrane proteins) Golgi apparatus (processing and sorting of secretory and membrane proteins for transport) 45 45  2024-09-20 Axons conducts electrical impulses (action potentials), generated at the cell body, to presynaptic terminal single, often very long process (>1 m in some large animals) carries proteins (synthesized at cell body) to presynaptic terminals insulated by myelin (specialized glial cells) Schwann cells in periphery oligodendrocytes in the CNS - gaps at regular intervals along myelin sheath (nodes of Ranvier) - function of myelin sheath: to ↑ the speed of action potential propagation 46 46  2024-09-20 Presynaptic Terminal ▪ transmits signal (via a neurotransmitter) to adjacent cell when electrical impulses arrive contains synaptic vesicles filled with neurotransmitters Synapse: site of contact between presynaptic terminal and adjacent cell 1) presynaptic terminal 2) receptive surface of the postsynaptic cell 3) the space in between (synaptic cleft) 47 47  2024-09-20 The Synapse (Chemical) Synapse: the space between two neurons or between a neuron and a receptor synaps/o, synapt/o Neurotransmitters: chemical substances released into the space to allow information to be relayed. Synaptic transmission: perpetuation of the impulse from the neuron to the next cell. 48 48  2024-09-20 The Chemical Synapse Neurotransmitters are released from the axon terminal of the presynaptic membrane into the synapse where they combine with receptors on the postsynaptic membrane Presynaptic terminal Synaptic cleft Postsynaptic cell 49 49  2024-09-20 Cell to Cell Conduction: the Synapse Types of Synapses: a) Electrical synapses: gap junctions very fast conduction; (eg cardiac muscle) b) Chemical synapses: involves the synthesis and release of neurotransmitters Once the action potential reaches the end of the axon, the information must be conveyed to the next neuron, or cells of the target organ or tissue 50 50