Presentation on theme: "CHAPTER 34 ORGANIZATION AND CONTROL OF NEURAL FUNCTION Essentials of Pathophysiology."— Presentation transcript:
CHAPTER 34 ORGANIZATION AND CONTROL OF NEURAL FUNCTION Essentials of Pathophysiology
PRE LECTURE QUIZ The dorsal horn cell columns contain the afferent (sensory) neurons and the ventral horn cell columns contain the efferent neurons. The brain is divided into three regions: the hindbrain, the midbrain, and the forebrain. The parasympathetic nervous system functions in maintaining vital functions and responding when there is a critical threat to the integrity of the individual—the “fight-or-flight” response. The blood-brain barrier and the cerebrospinal fluid–brain barrier protect the brain from substances in the blood that would disrupt brain function. Cerebrospinal fluid helps maintain a constant ionic environment that serves as a medium for diffusion of nutrients, electrolytes, and metabolic end products into the extracellular fluid surrounding central nervous system neurons and glia. T T F T T
PRE LECTURE QUIZ ______________ are the functioning cells of the nervous system. The _________________ nervous system contains two divisions: sympathetic and parasympathetic. Inside the skull and vertebral column, the brain and spinal cord are loosely suspended and protected by several connective tissue sheaths called the _________________. Neurons communicate with each other through structures known as ________________, of which there are two types: electrical and chemical. The main ___________________ for the autonomic nervous system are acetylcholine and the catecholamines, epinephrine and norepinephrine, which control neural function by selectively causing excitation or inhibition of action potentials. Autonomic meninges Neurons neurotransmitters synapses
NEURONS Dendrites receive stimuli Stimuli pass down axons Schwann cells contain myelin (“white matter”) Help increase speed of impulse transmission
SUPPORTING CELLS Peripheral nervous tissue Schwann cells: wrap a layer of myelin around axons Satellite cells: separate nervous cells from supporting tissue Central nervous tissue Oligodendroglia: myelinating cells Astroglia: regulate ion content in intercellular fluid Microglia: phagocytes Ependymal cells: line the neural tube cavity
IDENTIFY Microglial cell Neuron Oligodendritic cell Ependymal cell Astrocyte What is the function of each? E D C B A
QUESTION Tell whether the following statement is true or false. All neurons are myelinated.
ANSWER False Rationale: The myelin sheath increases the speed of impulse transmission (the impulse can skip over the myelinated/insulated parts of the neuron), but speed is not important everywhere (like the digestive tract). If every neuron was myelinated, neurons would take up a lot more space, too.
THE BASICS OF CELL FIRING Stimulus opens Na + gates At threshold, more Na+ gates open Na+ enters cell: depolarization K+ gates open K+ diffuses out: repolarization Threshold potential Resting membrane potential Stimulus Action potential
SYNAPTIC TRANSMISSION What is happening at stages 1–4? What will result if you block stage 2? Stage 3? Stage 4?
NEURON SECRETIONS Neurotransmitters Amino acids Peptides Monoamines Neuromodulators Attach to receptors and change their response to neurotransmitters Neurotrophic factors Neuron survival and to develop connections between neurons
GENERAL ORGANIZATION OF THE NERVOUS SYSTEM Begins as a hollow tube First segments of the tube become the brain Forebrain Midbrain Hindbrain
ORGANIZATION OF THE SPINAL CORD Dorsal Afferent Sensory Ventral Efferent Motor
SCENARIO A woman developed polyneuropathy. Her spinal nerves were damaged She lost the ability to tell where her body was positioned She has to look every time she takes a step, to tell where she is moving her feet to Question: What parts of her spinal nerves were damaged?
CELL COLUMNS OF THE SPINAL CORD What problems would you expect in someone who suffered ischemia to: Area A Area B Area C A B C
QUESTION If you place your hand on a hot surface, which ganglion carries the impulse to the spinal cord? a. Ventral b. Dorsal c. Interneuron d. Association neuron
Answer b. Dorsal Rationale: Afferent neurons carry sensory impulses to the spinal cord through the dorsal root ganglion; efferent neurons carry motor responses through the ventral root ganglion to effector cells in the tissue.
LAYERS OF THE WHITE MATTER Archi layer Connects neighboring segments Contains neurons reticular activating system Paleo layer Fibers reach to the brain stem Neo layer Pathways for bladder control and fine motor skills Develop by fifth year of life
FUNCTIONS OF THE HINDBRAIN Medulla oblongata, cerebellum, and pons Reflex centers for heart and respiration rates, coughing, swallowing, vomiting, etc. Gives rise to cranial nerves V–XII controlling viscera, hearing, facial, and mouth/throat functions Cerebellum allows fine motor coordination
FUNCTIONS OF THE MIDBRAIN Cerebral peduncles carry nerve fibers from the cerebrum to the hindbrain Cerebral aqueduct lets cerebrospinal fluid drain from the fourth ventricle inside the cerebrum Superior colliculi control reflex eye movements Inferior colliculi control reflex reactions to sound Gives rise to cranial nerves III and IV, controlling eye movement
FUNCTIONS OF THE FOREBRAIN Thalamus: “switchboard” or relay station for impulses going to and coming from the cerebrum Hypothalamus: homeostatic control Cerebrum Gives rise to cranial nerves I and II, for smell and sight
QUESTION Which part of the brain maintains vital functions like breathing, heart rate, and digestion? a. Forebrain b. Midbrain c. Hindbrain d. Cerebellum
ANSWER c. Hindbrain Rationale: Also known as the brain stem, this is the vasomotor center that controls cardiopulmonary function and digestion.
DURA MATER Has two layers Inner layer bends over to form a fold (falx cerebri) that separates the cerebral hemispheres It forms a second fold (tentorium) that holds the cerebrum up off the cerebellum
DURA MATER (CONT.) Between the layers of the dura, at the base of each fold, venous blood drains out of the brain in a sinus Bridging veins carry blood from the brain across the inner layer of the dura mater to the sinus The sinus also collects cerebrospinal fluid
ARACHNOID Lies just beneath the dura mater Waterproof Cerebrospinal fluid (CSF) lies under the arachnoid to cushion the brain Extensions of the arachnoid (villi) poke through the inner layer of the dura mater into the sinuses, to let CSF drain into the sinuses
PIA MATER Lies right on the surface of the brain Holds the cerebral arteries in place
MENINGES AND MENINGEAL SPACES Epidural space: meningeal arteries Dura mater Subdural space: bridging veins Arachnoid Subarachnoid space: cerebral arteries, cerebrospinal fluid Pia mater
CEREBROSPINAL FLUID Leaks out of capillaries inside the brain’s hollow ventricles Composition controlled by the blood-brain barrier Passes out an opening below the cerebellum Circulates around the brain and spinal cord in the subarachnoid space Passes through arachnoid villi into blood in the dural sinuses and is returned to the heart
AUTONOMIC NERVOUS SYSTEM Sympathetic Catecholamines Epinephrine, norepinephrine, dopamine Attach to adrenergic receptors Parasympathetic Acetylcholine Attaches to cholinergic receptors
ADRENERGIC NEUROTRANSMITTERS Synthesized in the sympathetic system Attach to adrenergic receptors Alpha-1 receptors: constrict blood vessels Alpha-2 receptors: negative feedback to stop neurotransmitter release Beta-1 receptors: speed and strengthen heart Beta-2 receptors: bronchodilation Neurotransmitter is removed from synapse by reuptake or degraded by enzymes
CHOLINERGIC NEUROTRANSMITTER— ACETYLCHOLINE Released from parasympathetic system and from motor neurons Attaches to cholinergic receptors Nicotinic receptors: excite skeletal muscle cells Muscarinic receptors: slow heart, stimulate GI tract, vasodilate Neurotransmitter is removed from synapse by acetylcholinesterase
QUESTION Tell whether the following statement is true or false. The sympathetic division of the ANS is also known as fight-or-flight.
ANSWER True Rationale: The SNS is characterized by the release of adrenaline, which results in pupil dilation, bronchodilation, and increased HR, BP, and glucose production—all the things that come in handy when you are running from something!