Nervous Tissue Flashcards
Fully discuss the three basic functions of the nervous system.
Sensory Function (afferent) -
- a sensory receptor picks up a stimulus which can be either internal or external
- It then gets carried into the CNS through cranial and spinal nerves
2) Integrative Function (process)
- responsible for processing sensory input then makes a decision in response
- known as integration
3) Motor Function (efferent)
- once integration is complete a motor response actives an effector (muscles and glands), through cranial and spinal nerves
- this causes glands to secrete or muscles to contract.
Describe the organization and structure of the nervous system.
The CNS (central nervous system)
- receives sensory input and sends out motor output all which comes through the PNS (peripheral nervous system)
CNS contains the brain and spinal cord
The PNS contains cranial and spinal nerves, enteric plexus, and sensory receptors in the skin.
The PNS is separated into 2 divisions:
- Sensory Division: (to the CNS)
- Somatic Senses.
- Special Senses
- Motor Division: (from the CNS)
- Somatic Nervous System: specifically targets skeletal muscles
- Autonomic Nervous system composed of 3 systems
- Sympathetic System -smooth muscle, cardiac muscle, and glands
- Parasympathetic System -smooth muscle, cardiac muscle, and glands
- Enteric Nervous System -smooth muscle and glands of the GI tract
Describe the structure of a neuron.
Nerve Cells can be broken into 3 parts. Cell Body, Dendrites, and Axon
- Cell Body is composed of
- nucleus
- cytoplasm
- mitochondria
- lysosomes
- Golgi complex
- rough endoplasmic reticulum
- neurofibrils
- Dendrites
- short, tapering, and highly branched forming a tree shape array of processes that emerge from the cell
- they are the input part of the neuron
- Axon
- conducts nerve impulses toward another neuron, muscle cell or glandular cell.
- Long cylindrical projection that joins a cell body at the axon hillock cone-shaped part
- impulse begin at the axon hillock and travel along the axon
- the end of axons have fine processes called Axon terminals
- the tip of the axon terminal ends in a bell-shaped ending called a synaptic end bulb.
- the synaptic end bulb contain synaptic vesicles which store neurotransmitters
What is a synapse?
The site where communication can occur between 2 neurons or a neuron and an effector cell
Define neuroglia; list its six types; and state their function.
Neuroglia are specialized tissue cells that
- support neurons
- attach neuron blood vessels
- produce the myelin sheath around axons
- carry out phagocytosis.
6 type of Neuroglia:
4 found in the CNS are s to
- Astrocytes: blood-brain barrier
- Oligodendrocytes: Support
- Microglial Cells: phagocytosis
- Ependymal Cells: cerebrospinal fluid (CSF) production
2 are found in the PNS
- Schwann Cells: myelin production
- Satellite cells: support neurons in PNS ganglia
Describe the production and function of myelin.
Myelin Sheath: is a multilayered lipid and protein covering which surrounds an axon of a neuron.
Function:
- insulates the axon to increase the speed of nerve impulse conductivity
Production:
- Schwann cells in the PNS and Oligodendrocytes in CNS are responsible for creating the myelin sheath
- they wrap themselves around the axon creating up to 100 layers covering the axon
What are the two types of axons?
Unmyelinated - do not have a myelin sheath
Myelinated - have a myelin sheath surrounding them
What are the nodes of Ranvier?
Gaps in the myelin sheath that appear at intervals along the axon of a nerve.
Compare and contrast the structure of white matter and gray matter in the central nervous system (CNS).
White Matter:
- contains myelinated axons
- myelin sheath appear white which gives it the colour
Gray Matter:
- Gray colour comes from a lack of myelin and due to cellular organelles
- contains neuronal cell bodies, dendrites, unmyelinated axons, axon terminals and neuroglia
In the spinal cord, gray matter forms an H-shaped inner core, which is surrounded by white matter; in the brain, a thin outer shell of gray matter covers the cerebral hemispheres.
A nucleus region of gray matter in the CNS, surrounded by white matter, consists of a mass of nerve cell bodies and dendrite
Describe the cellular properties that permit communication among neurons and effectors.
Excitable cells communicate with each other by action potentials or graded potentials.
Action potentials allow communication over short and long distances, whereas graded potentials allow communication only over short distances.
The production of both types of potentials depends on the existence of a resting membrane potential and the presence of certain types of ion channels. A membrane potential is an electrical voltage across the membrane. Graded and action potentials occur because the ion channels in a membrane allow ion movement across the membrane that can change the membrane potential.
The two basic types of ion channels are leakage (nongated) and gated. Leakage (nongated) channels are always open. Gated channels open and close in response to some sort of stimulus.
Gated ion channels respond to voltage changes, ligands (chemicals), and mechanical pressure.
Voltage-gated ion channels respond to a direct change in the membrane potential.
Ligand-gated ion channels respond to a specific chemical stimulus (not discussed in your textbook).
Mechanically-gated ion channels respond to mechanical vibration or pressure (not discussed in your textbook).
Describe the factors that maintain a resting membrane potential.
The membrane of a non-conducting neuron is positive outside and negative inside due to the distribution of different ions across the membrane, and the relative permeability of the membrane toward Na+ and K+.
A typical value for the resting membrane potential is -70 millivolts (mV), which means that the membrane is polarized.
The resting membrane potential is determined by the unequal distribution of ions across the plasma membrane, and the selective permeability of the membrane to Na+ and K+.
Sodium-potassium pumps compensate for the slow leakage of Na+ into the cell by pumping it back out.
List and explain the events involved in the generation of an action potential in a neuron.
An action potential (AP) or impulse is a sequence of rapidly occurring events that decrease and eventually reverse the membrane potential (depolarization), which is followed by the restoration of the resting membrane potential (repolarization).
During an action potential, voltage-gated Na+ and K+ channels open in sequence. The rapid opening of voltage-gated Na+ channels causes depolarization. If the depolarization is to the threshold, the membrane potential reverses.
Depolarization occurs due to the interaction of the two voltage-gated Na+ channel gates: an activation gate and an inactivation gate.
The slower opening of the voltage-gated K+ channels and the closing of the previously open Na+ channels leads to a repolarization, the recovery of the resting membrane potential.
During the refractory period, another impulse cannot be generated (absolute refractory period) or can be triggered only by a suprathreshold stimulus (relative refractory period).
An action potential conducts or propagates (travels) from point to point along the membrane; the travelling action potential is a nerve impulse.
According to the all-or-none principle, if a stimulus is strong enough to generate an action potential, the impulse travels at a constant and maximum strength during the existing conditions; a stronger stimulus does not cause a larger impulse.
Define the refractory period
The refractory period is the time an excitable membrane takes to be able to respond to a second stimulus once it has returned to its resting state.
Describe the conduction of an impulse.
The step-by-step depolarization of each adjacent area of the plasma membrane is called continuous conduction.
Nerve impulse conduction, in which an impulse jumps from neurofibral node to node, is called saltatory conduction.
The propagation speed of a nerve impulse is not related to stimulus strength; rather, it is related to
- Larger-diameter fibres conduct impulses faster than those with smaller diameters
- Myelinated fibres conduct impulses faster than unmyelinated fibres
- Nerve fibres conduct impulses faster when warmed, and slower when cooled
Saltatory conduction occurs along a myelinated axon. The impulse jumps from node to node.
Discuss the events of signal transmission at a synapse.
A synapse is a functional junction between one neuron and another or between a neuron and an effector—for example, a muscle or gland.
Synaptic Events
- An impulse arrives at the end bulb of an axon.
- Calcium channels open on the end bulb, and calcium flows in.
- Neurotransmitters are released into the synaptic gap.
- Neurotransmitters bind to receptors on the postsynaptic neuron and open ion channels.
- The open ion channels allow other ions to enter, and this process triggers an impulse in the postsynaptic neuron.
Neurotransmitters are removed from the synaptic cleft in the following three ways:
- Diffusion
- Enzymatic degradation
- Uptake into cells (neurons and glia)
