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 thefunction of each?
QuestionTell whether the following statement is true or false.All neurons are myelinated.
False AnswerRationale: 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 Action potential• At threshold, more Na+ gates open Threshold• Na+ enters cell: potential depolarization• K+ gates open Resting• K+ diffuses out: membrane repolarization potential Stimulus
SynapticTransmission• What is happening at stages 1–5?• 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
Organization of the Spinal Cord• Dorsal – Afferent – Sensory• Ventral – Efferent – Motor
ScenarioA 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 toQuestion:• What parts of her spinal nerves were damaged?
Cell Columns of the Spinal Cord• What problems would you expect in A someone who B suffered ischemia C to: – Area A – Area B – Area C
QuestionIf you place your hand on a hot surface, which ganglion carries the impulse to the spinal cord?b. Ventralc. Dorsald. Interneurone. Association neuron
a. Dorsal AnswerRationale: 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
QuestionWhich part of the brain maintains vital functions like breathing, heart rate, and digestion?b. Forebrainc. Midbraind. Hindbraine. Cerebellum
a. Hindbrain AnswerRationale: 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
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
QuestionTell whether the following statement is true or false.The sympathetic division of the ANS is also known as fight-or-flight.
True AnswerRationale: 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!