Chapter 10: nervous system 1.
General functions of the nervous system.
1.The nervous system is composed of neural tissue, including neurons and neuroglial cells, blood vessels and connective tissue.
2.Organs of the nervous system are divided into the central and peripheral nervous systems.
3.Sensory receptors detect changes in internal and external body conditions.
4.The integrative functions bring sensory information together and make decisions that motor functions act upon.
5.Motor impulses stimulate effectors to respond.
6.The motor portion of the peripheral nervous system involved in voluntary activities is the somatic nervous system.
7.The motor portion of the peripheral nervous system involved in involuntary activities is the autonomic nervous system.
8.A neuron in includes a cell body, cell processes and the organelles usually found in cells.
9.Dendrites and the cell body provide receptive surfaces.
10.A single axon or rises from the cell body and maybe enclosed in a myelin sheath and a neurilemma.
Types of neurons.
1.Sensory neurons conducting nerve impulses from receptors in peripheral body parts into the brain or spinal cord.
2.Interneurons transmit nerve impulses between neurons within the brain and spinal cord.
3.Motor neurons conducting nerve impulses from the brain or spinal cord out to effectores-muscles or glands.
Types of neuronal glial cells
1.Astrocytes are star shaped cells between neurons in the blood vessels.
2.Astrocytes provide structural support, formation of scar tissue, transport substances between blood vessels and neurons, communicate with one another and with neurons, mop up excess ions in neurotransmitters, and induce synapse formation.
3.Oligodendrocytes form myelin sheaves within the brain and spinal cord, and produce nerve growth factors.
4.Microglia provide structural support and phagocytosis or immune protection.
5.Ependyma form a porous layer through which substances diffuse between the interstitial fluid of the brain and spinal cord and the cerebral spinal fluid.
6.Schwann cells are cells with abundant, lipid rich membranes that wrap tightly around the axons of peripheral neurons.
7.Schwann cells increase the speed of neurotransmission.
The synapse.
1.A synapse is a junction between two nerve cells.
2.A synaptic cleft is the gap between parts of two cells in the synapse.
3.Synaptic transmission is the process by which the impulse in the presynaptic neuron signals the postsynaptic cell.
4.If a graded impulse from a dendrite or cell body triggers an action potential, it then travels along the axons to a synapse.
5.Axons have synaptic knobs at the distal ends that secrete neurotransmitters.
6.The neurotransmitter is released whenever impulse reaches the end of axons, and the neurotransmitter defuses across the synaptic cleft.
7.A neurotransmitter reaching a postsynaptic neuron or other cell may be excitatory or inhibitory.
Cell membrane potential.
1.A cell membrane is usually polarized as a result of an unequal distribution of ions on either side of a membrane.
2.Channels in membranes that allow passage of some ions but not others control ion distribution.
Distribution of ions.
1.A high concentration of sodium ions is on the outside of the membrane, and a high concentration of potassium ions is on the inside of the cell.
2.The difference in ion concentration across the cell membrane, and the resulting membrane potential, is maintained by sodium-potassium pumps.
3.The maintenance of normal resting potential of a nerve cell requires ATP to drive the sodium-potassium pumps.
Resting potential.
1.Large numbers of negatively charged ions, which cannot diffuse through the cell membrane, are inside the nerve cell.
2.Interesting nerve cell, more positive ions leave the cell and enter it, so the inside of the cell membrane develops a negative charge with respect to the outside.
Local potential changes.
1.Stimulation of in membrane affects its resting potential in the local region.
2.The nerve cell membrane is depolarized if it becomes less negative.
3.The nerve cell membrane is hyperpolarized if it becomes more negative.
4.Reaching threshold potential triggers an action potential.
Action potentials.
1.At threshold, sodium channels open and sodium ions diffuse inward, depolarizing the membrane.
2.Slightly later, potassium channels open and potassium ions diffuse outward, repolarizing the cell membrane.
3.The rapid change in cell membrane potential is called an action potential.
4.Many action potentials can occur before active transport reestablishes the original resting potential.
5.The propagation of action potentials along a nerve fiber is called an impulse.
All or none response.
1.A nerve impulses and all or none response.
2.If a stimulus of threshold intensity is not applied to an axon, and action potential is not generated.
Refractory period.
1.The refractory period is a brief time following passage of the nerve impulse when the membrane is unresponsive to an ordinary stimulus.
2.During the absolute refractory period, the membrane cannot be stimulated.
3.During the relative refractory period, the membrane can be stimulated with a higher intensity stimulus.
Impulse conduction.
1.An unmyelinated axon conducts impulses that travel over its entire surface.
2.A myelinated axon conducts impulses that travel from node to node.
3.Impulse conduction is more rapid on myelinated axons with large diameters.
4.In a nerve impulse traveling along a myelinated axon, action potentials occur only at the nodes.
5.Action potentials in myelinated axons appears to jump from node to node and is thus referred to as saltatory conduction.
Events leading to nerve impulse conduction.
1.Nerve cell membrane maintains resting potential by diffusion of sodium and potassium ions down there concentration gradients as the cell pumps them up the gradients.
2.Neurons receive stimulation, causing local potentials, which may sum to reach threshold.
3.Sodium channels in the local region of the membrane open.
4.Sodium ions diffuse inward, depolarizing the membrane.
5.Potassium channels in the membrane open.
6.Potassium ions diffuse outward, repolarizing the membrane.
7.The resulting action potential causes an electric current that stimulates an adjacent portions of the membrane.
8.Action potentials occur sequentially along the length of the axon as a nerve impulse.
General functions of the nervous system.
1.The nervous system is composed of neural tissue, including neurons and neuroglial cells, blood vessels and connective tissue.
2.Organs of the nervous system are divided into the central and peripheral nervous systems.
3.Sensory receptors detect changes in internal and external body conditions.
4.The integrative functions bring sensory information together and make decisions that motor functions act upon.
5.Motor impulses stimulate effectors to respond.
6.The motor portion of the peripheral nervous system involved in voluntary activities is the somatic nervous system.
7.The motor portion of the peripheral nervous system involved in involuntary activities is the autonomic nervous system.
8.A neuron in includes a cell body, cell processes and the organelles usually found in cells.
9.Dendrites and the cell body provide receptive surfaces.
10.A single axon or rises from the cell body and maybe enclosed in a myelin sheath and a neurilemma.
Types of neurons.
1.Sensory neurons conducting nerve impulses from receptors in peripheral body parts into the brain or spinal cord.
2.Interneurons transmit nerve impulses between neurons within the brain and spinal cord.
3.Motor neurons conducting nerve impulses from the brain or spinal cord out to effectores-muscles or glands.
Types of neuronal glial cells
1.Astrocytes are star shaped cells between neurons in the blood vessels.
2.Astrocytes provide structural support, formation of scar tissue, transport substances between blood vessels and neurons, communicate with one another and with neurons, mop up excess ions in neurotransmitters, and induce synapse formation.
3.Oligodendrocytes form myelin sheaves within the brain and spinal cord, and produce nerve growth factors.
4.Microglia provide structural support and phagocytosis or immune protection.
5.Ependyma form a porous layer through which substances diffuse between the interstitial fluid of the brain and spinal cord and the cerebral spinal fluid.
6.Schwann cells are cells with abundant, lipid rich membranes that wrap tightly around the axons of peripheral neurons.
7.Schwann cells increase the speed of neurotransmission.
The synapse.
1.A synapse is a junction between two nerve cells.
2.A synaptic cleft is the gap between parts of two cells in the synapse.
3.Synaptic transmission is the process by which the impulse in the presynaptic neuron signals the postsynaptic cell.
4.If a graded impulse from a dendrite or cell body triggers an action potential, it then travels along the axons to a synapse.
5.Axons have synaptic knobs at the distal ends that secrete neurotransmitters.
6.The neurotransmitter is released whenever impulse reaches the end of axons, and the neurotransmitter defuses across the synaptic cleft.
7.A neurotransmitter reaching a postsynaptic neuron or other cell may be excitatory or inhibitory.
Cell membrane potential.
1.A cell membrane is usually polarized as a result of an unequal distribution of ions on either side of a membrane.
2.Channels in membranes that allow passage of some ions but not others control ion distribution.
Distribution of ions.
1.A high concentration of sodium ions is on the outside of the membrane, and a high concentration of potassium ions is on the inside of the cell.
2.The difference in ion concentration across the cell membrane, and the resulting membrane potential, is maintained by sodium-potassium pumps.
3.The maintenance of normal resting potential of a nerve cell requires ATP to drive the sodium-potassium pumps.
Resting potential.
1.Large numbers of negatively charged ions, which cannot diffuse through the cell membrane, are inside the nerve cell.
2.Interesting nerve cell, more positive ions leave the cell and enter it, so the inside of the cell membrane develops a negative charge with respect to the outside.
Local potential changes.
1.Stimulation of in membrane affects its resting potential in the local region.
2.The nerve cell membrane is depolarized if it becomes less negative.
3.The nerve cell membrane is hyperpolarized if it becomes more negative.
4.Reaching threshold potential triggers an action potential.
Action potentials.
1.At threshold, sodium channels open and sodium ions diffuse inward, depolarizing the membrane.
2.Slightly later, potassium channels open and potassium ions diffuse outward, repolarizing the cell membrane.
3.The rapid change in cell membrane potential is called an action potential.
4.Many action potentials can occur before active transport reestablishes the original resting potential.
5.The propagation of action potentials along a nerve fiber is called an impulse.
All or none response.
1.A nerve impulses and all or none response.
2.If a stimulus of threshold intensity is not applied to an axon, and action potential is not generated.
Refractory period.
1.The refractory period is a brief time following passage of the nerve impulse when the membrane is unresponsive to an ordinary stimulus.
2.During the absolute refractory period, the membrane cannot be stimulated.
3.During the relative refractory period, the membrane can be stimulated with a higher intensity stimulus.
Impulse conduction.
1.An unmyelinated axon conducts impulses that travel over its entire surface.
2.A myelinated axon conducts impulses that travel from node to node.
3.Impulse conduction is more rapid on myelinated axons with large diameters.
4.In a nerve impulse traveling along a myelinated axon, action potentials occur only at the nodes.
5.Action potentials in myelinated axons appears to jump from node to node and is thus referred to as saltatory conduction.
Events leading to nerve impulse conduction.
1.Nerve cell membrane maintains resting potential by diffusion of sodium and potassium ions down there concentration gradients as the cell pumps them up the gradients.
2.Neurons receive stimulation, causing local potentials, which may sum to reach threshold.
3.Sodium channels in the local region of the membrane open.
4.Sodium ions diffuse inward, depolarizing the membrane.
5.Potassium channels in the membrane open.
6.Potassium ions diffuse outward, repolarizing the membrane.
7.The resulting action potential causes an electric current that stimulates an adjacent portions of the membrane.
8.Action potentials occur sequentially along the length of the axon as a nerve impulse.
Chapter 11: nervous system 2
Introduction.
1.Bone and protected membranes called meninges surround the brain and spinal cord.
Meninges.
1.The meninges consists of a dura mater, arachnoid mater, pia mater.
2.Cerebral spinal fluid occupies the space between the arachnoid and pia maters.
Ventricles and cerebrospinal fluid.
1.Ventricles are connected cavities within the cerebral hemispheres and brainstem.
2.Cerebrospinal fluid fills the ventricles.
3.Choroid plexuses in the walls of the ventricles secrete cerebrospinal fluid.
4.Ependymal cells of the choroid plexus regulate the composition of cerebral spinal fluid.
5.Cerebrospinal fluid circulates through the ventricles and is reabsorbed into the blood of the dural sinuses.
Spinal cord.
1.The spinal cord is a nerve column that extends from the brain into the vertebral canal.
2.The spinal cord terminates at the level between the first and second lumbar vertebrae.
3.The spinal cord is the center for spinal reflexes.
4.Reflexes are autonomic, subconscious responses to changes.
5.Spinal reflexes help maintain homeostasis.
6.The knee-jerk reflex employs only two neurons.
7.Withdrawal reflexes are protective actions.
8.The spinal cord provides a two-way communication system between the brain and structures outside the nervous system.
9.Ascending tracts carry sensory impulses to the brain.
10.Descending tracts carry motor impulses to muscles and glands.
11.Many of the fibers in the ascending and descending tracts cross over in the spinal cord or brain.
Brain.
1.The brain is the largest and most complex part of the nervous system.
2.The brain contains nerve centers that are associated with sensations.
3.The brain issues motor commands and carries on higher mental functions.
Brain development.
1.The brain develops from a neural tube with three cavities-the forebrain, midbrain, and hindbrain.
Structure of the cerebrum.
1.The cerebrum consists of two cerebral hemispheres connected by the corpus callosum.
2.The cerebral surfaces marked by ridges and grooves.
3.Sulci divide each brain hemisphere into lobes.
4.The cerebral cortex is a thin layer of gray matter near the surface.
5.White matter consists of myelinated nerve fibers that interconnect neurons with the nervous system and communicate with other body parts.
Functions of the cerebral.
1.The cerebrum is concerned with higher brain functions, such as thought, reasoning, interpretation of sensory impulses, control involuntary muscles, and memory storage.
Basal nuclei.
1.Basal nuclei are masses of gray matter located deep within the cerebral hemispheres.
2.The neurons of the basal nuclei interact with other brain areas to facilitate voluntary movement.
Diencephalon.
1.The diencephalon contains the thalamus and the hypothalamus.
2.The thalamus selects incoming sensory impulses and relays them to the cerebral cortex.
3.The hypothalamus is important in maintaining homeostasis.
Brainstem.
1.The brainstem extends from the base of the brain to the spinal cord.
2.The brainstem consists of the midbrain, pons, and the medulla oblongata.
3.The reticular formation filters incoming sensory impulses, arousing the cerebral cortex into wakefulness in response to meaningful impulses.
4.Normal sleep results from decreasing activity of the reticular formation, and paradoxical sleep occurs when activating impulses are received from some parts of the brain, but not by others.
Cerebellum.
1.The cerebellum consists of two hemispheres connected by the vermis.
2.The cerebellum functions primarily as a reflex center, coordinating skeletal muscle movements and maintaining equilibrium.
Peripheral nervous system.
1.The peripheral nervous system consists of cranial and spinal nerves that branch out from the brain and spinal cord to all body parts.
2.The peripheral nervous system can be subdivided into somatic and autonomic portions.
Structure of peripheral nerves.
1.A nerve consists of a bundle of nerve fibers surrounded by connective tissues.
Nerve and nerve fiber classification.
1.Nerves are cord like bundles of nerve fibers.
2.Nerves can be classified as sensory nerves, motor nerves, or mixed nerves, depending on which type of fibers they contain.
3.Nerve fibers within the central nervous system can be subdivided into groups with general and special functions.
Cranial nerves.
1.12 pairs of cranial nerves connect the brain to parts in the head, neck, and trunk.
CN I is the olfactory nerve
CN II is the optic nerve
CN III is the occulomotor nerve
CN IV is the trochlear nerve
CN V is the trigeminal nerve and gives sensation over the face
CN VI is the abducens nerve
CN VII is the facial nerve which innervates the muscles of the face
CN VIII is the vestibulocochlear nerve
CN IX is the glossopharyngeal nerve
CN X is the vagus nerve
CN XI is the accessory nerve
CN XII is the hypoglossal nerve
Spinal nerves.
1.31 pairs of spinal nerves originate from the spinal cord.
2.Spinal nerves provide a two-way communication system between the spinal cord and the upper limbs, lower limbs, neck, and trunk.
3.Each spinal nerve emerges by a dorsal root in the ventral root.
4.A dorsal root contain sensory fibers and has a dorsal root ganglion.
5.A ventral root contains motor fibers.
Autonomic nervous system.
1.The autonomic nervous system functions without conscious effort.
2.The autonomic nervous system is concerned primarily with regulating visceral activities that maintain homeostasis.
3.Autonomic functions are reflexes control from centers in the hypothalamus, brainstem, and spinal cord.
4.Autonomic nerve fibers are associated with ganglia where impulses are integrated before distribution to effectors.
5.The integrative function of the ganglia provides a degree of independence from the central nervous system.
6.The autonomic nervous system is divided into two divisions-sympathetic and parasympathetic.
7.The sympathetic division prepares the body for stressful and emergency conditions.
8.The parasympathetic division is most active under ordinary conditions.
10.Autonomic neurotransmitters.
11.Sympathetic and parasympathetic preganglionic fibers secrete acetylcholine.
12.Most sympathetic postganglionic fibers secrete norepinephrine and are adrenergic.
13.Postganglionic parasympathetic fibers secrete acetylcholine and are cholinergic.
14.The different effects of the autonomic divisions are due to the different neurotransmitters the postganglionic fibers release.
Actions of autonomic neurotransmitters.
1.Neurotransmitters combine with receptors and alter cell membranes.
2.Acetylcholine acts very briefly.
3.Norepinephrine and epinephrine may have more prolonged effects.
Control of autonomic activity.
1.The central nervous system largely controls the autonomic nervous system.
2.The medulla oblongata uses autonomic fibers to regulate cardiac, vasomotor, and respiratory activities.
3.The hypothalamus uses autonomic fibers in regulating visceral functions.
4.The limbic system and the cerebral cortex control emotional responses to the autonomic nervous system.
Spinal nerves.
1.31 pairs of spinal nerves originate from the spinal cord.
2.Spinal nerves provide a two-way communication system between the spinal cord and the upper limbs, lower limbs, neck, and trunk.
3.Each spinal nerve emerges by a dorsal root in the ventral root.
4.A dorsal root contain sensory fibers and has a dorsal root ganglion.
5.A ventral root contains motor fibers.
Autonomic nervous system.
1.The autonomic nervous system functions without conscious effort.
2.The autonomic nervous system is concerned primarily with regulating visceral activities that maintain homeostasis.
3.Autonomic functions are reflexes control from centers in the hypothalamus, brainstem, and spinal cord.
4.Autonomic nerve fibers are associated with ganglia where impulses are integrated before distribution to effectors.
5.The integrative function of the ganglia provides a degree of independence from the central nervous system.
6.The autonomic nervous system is divided into two divisions-sympathetic and parasympathetic.
7.The sympathetic division prepares the body for stressful and emergency conditions.
8.The parasympathetic division is most active under ordinary conditions.
10.Autonomic neurotransmitters.
11.Sympathetic and parasympathetic preganglionic fibers secrete acetylcholine.
12.Most sympathetic postganglionic fibers secrete norepinephrine and are adrenergic.
13.Postganglionic parasympathetic fibers secrete acetylcholine and are cholinergic.
14.The different effects of the autonomic divisions are due to the different neurotransmitters the postganglionic fibers release.
Actions of autonomic neurotransmitters.
1.Neurotransmitters combine with receptors and alter cell membranes.
2.Acetylcholine acts very briefly.
3.Norepinephrine and epinephrine may have more prolonged effects.
Control of autonomic activity.
1.The central nervous system largely controls the autonomic nervous system.
2.The medulla oblongata uses autonomic fibers to regulate cardiac, vasomotor, and respiratory activities.
3.The hypothalamus uses autonomic fibers in regulating visceral functions.
4.The limbic system and the cerebral cortex control emotional responses to the autonomic nervous system.
