Nervous System (Flashcards)
What is the primary function of the nervous system?
To monitor internal and external changes, integrate information, and generate precise responses to maintain homeostasis
What are the two main types of cells in the nervous system?
Neurons and glial cells. Neurons transmit electrical signals, and glial cells support and protect neurons.
What creates the electrochemical gradients in cells?
Differences in the concentration of ions and molecules between intracellular and extracellular fluids
What is a nerve impulse?
An electrical signal that is generated and propagated along the axon of a neuron
List the important ions involved in establishing electrochemical gradients
K+, Na+, Cl-, Ca++, and large negatively charged organic ions (org-).
How is the resting membrane potential (RMP) established and maintained?
- Na+/K+-ATPase (sodium-potassium pump) maintains ion concentration gradients
- Non-gated K+ channels make the membrane more permeable to K+ at rest
- Large, negatively charged organic ions (org-) inside the cell.
Define graded potentials (GPs)
Small changes in the resting membrane potential, usually occurring on dendrites or the cell body, caused by the opening of gated ion channels
What are the different types of gated ion channels?
- Voltage-gated channels: open in response to membrane voltage changes.
- Chemically-gated channels: open in response to chemical binding (e.g., neurotransmitters).
- Temperature-gated channels: open in response to temperature changes.
- Mechanically-gated channels: open in response to mechanical deformation.
What is the approximate value of the resting membrane potential (RMP)?
Approximately -70 mV (inside of the cell is more negative).
What are the possible results of graded potentials?
- Depolarization:
- Membrane potential becomes more positive than RMP (e.g., -70 mV to -65 mV).
- Hyperpolarization:
- Membrane potential becomes more negative than RMP (e.g., -70 mV to -75 mV).
What is the relationship between graded potentials and action potentials?
If a graded potential causes sufficient depolarization to reach the threshold potential, it can trigger an action potential
Define action potential (AP)
A large, rapid change in membrane potential that propagates along the axon of a neuron
List the phases of an action potential
- Depolarization phase
- Repolarization phase
- After-hyperpolarization phase
What is the role of voltage-gated Na+ channels in the action potential?
They open in response to membrane potential changes, increasing Na+ permeability and causing depolarization
What is the role of voltage-gated K+ channels in the action potential?
They open during repolarization, increasing K+ permeability and allowing K+ to diffuse out of the cell, decreasing the membrane potential
What is the absolute refractory period?
A period during which no action potential can be generated, regardless of stimulus size, due to all Na+ channels being either open or inactivated
What is the relative refractory period?
A period during which an action potential can be generated, but only by a greater than normal stimulus, because Na+ channels are reactivated but K+ channels are still open.
What is synaptic transmission?
The process by which a presynaptic neuron communicates with a postsynaptic neuron via a synapse
How does myelination affect the rate of action potential propagation?
Myelinated fibers propagate action potentials faster due to saltatory conduction, where action potentials occur only at the nodes of Ranvier
State the all-or-none principle of action potentials
If the threshold is reached, an action potential is produced with the same maximum depolarization. Below the threshold, no action potential occurs
Compare Type A and Type C nerve fibers
- Type A:
- Large diameter, myelinated, fast propagation (~130 m/sec), found in sensory and motor neurons.
- Type C:
- Small diameter, unmyelinated, slow propagation (~0.5 m/sec), found in the autonomic nervous system and some pain fibers.
List the steps of synaptic transmission
- Action potential arrives at the axon terminal.
- Voltage-gated Ca++ channels open, and Ca++ enters the axon terminal.
- Increase in Ca++ triggers exocytosis of neurotransmitter (nt) containing vesicles.
- Neurotransmitter diffuses across the synaptic cleft and binds to receptors on the postsynaptic membrane.
- Gated ion channels open, causing a graded potential (postsynaptic potential).
What are the two types of postsynaptic potentials (PSPs)?
- Excitatory PSPs (EPSPs): cause depolarization.
- Inhibitory PSPs (IPSPs): cause hyperpolarization.
Describe synaptic transmission at the neuromuscular junction
- Neurotransmitter released is always acetylcholine (ACh).
- ACh binds to chemical gates on the muscle motor end plate, causing a graded potential (end plate potential, EPP).
- EPP triggers an action potential on the sarcolemma.
How do receptors detect stimuli?
Receptors respond to specific stimuli by opening gated channels (usually Na+), causing a graded potential on the receptor membrane.
What are the two types of graded potentials that can occur on a receptor membrane?
- Generator potential:
- occurs on dendrites of a first-order sensory neuron and directly generates an action potential.
- Receptor potential:
- occurs on a separate receptor cell, causing the release of neurotransmitter onto the sensory neuron.
What are phasic receptors?
Receptors that respond to stimulus change and show adaptation (decrease in sensitivity) in the presence of a constant stimulus.
What are tonic receptors?
Receptors that maintain a constant action potential frequency in the presence of a constant stimulus, providing continuous monitoring
How does the brain perceive different types of stimuli?
Mainly by the type of receptor stimulated and the specific neural pathway to the CNS
What is a reflex?
A rapid, automatic response to a stimulus that always causes the same motor response and usually involves two or more neurons.
How does the brain perceive stimuli of different strengths?
Mainly by the frequency of action potentials going to the CNS. Stronger stimuli also activate more receptors.
Differentiate between somatic and visceral reflexes.
- Somatic reflex:
- effector is skeletal muscle.
- Visceral (autonomic) reflex:
- effector is smooth muscle, cardiac muscle, or glands.
What is a monosynaptic reflex?
A reflex arc involving one synapse between one sensory and one motor neuron
What is a polysynaptic reflex?
A reflex arc involving two or more synapses between three or more neurons
Describe the stretch reflex.
Automatic muscle contraction in response to sudden or excessive stretching, helping maintain muscle tone and stabilize posture.
Describe the flexor (withdrawal) reflex.
Automatic contraction of flexor muscles to move a body part away from a painful stimulus.
Describe the crossed extensor reflex
Automatic contraction of extensor muscles in the opposite limb during a withdrawal reflex, maintaining balance.
What are the main functions of the brain stem?
Controls life-sustaining processes such as breathing and circulation.
What are the major functions of the hypothalamus?
Regulates the autonomic nervous system, parts of the endocrine system, temperature, food and water intake, and is part of the limbic system (emotional brain).
What is reciprocal inhibition?
The inhibition of somatic lower motor neurons to antagonist muscles during contraction of an agonist muscle, ensuring smooth and coordinated movements
What are the main functions of the cerebrum?
Interprets sensory information, initiates and controls skeletal muscle movement, and is involved in higher functions like memory, intellect, and language
What are the two divisions of the autonomic nervous system (ANS)?
Sympathetic Nervous System (SNS) and Parasympathetic Nervous System (PSNS)
What is the function of the autonomic nervous system (ANS)?
Transmits signals from the CNS to autonomic effectors (smooth muscle, cardiac muscle, glands)
What are the two divisions of the motor nervous system?
- Autonomic Nervous System
- Somatic Nervous System
What is the general function of the parasympathetic nervous system (PSNS)?
Rest and digest; housekeeping
What is the general function of the sympathetic nervous system (SNS)?
Prepares the body for activity; fight or flight response.
What neurotransmitter do adrenergic neurons release?
Norepinephrine (NE).
What neurotransmitter do cholinergic neurons release?
Acetylcholine (ACh)
How is norepinephrine (NE) broken down?
Actively transported back into the synaptic end bulb and broken down by the enzyme monoamine oxidase (MAO).
What is the function of the somatic nervous system?
Transmits signals from the CNS to skeletal muscle.
How is acetylcholine (ACh) broken down?
By the enzyme acetylcholinesterase (AChE) on the postsynaptic membrane.
List the levels of motor control.
- Planning
- Signaling directly to lower motor neurons
- Brain stem nuclei coordinating large muscle groups
- Spinal cord is setting rhythmic movements
- Cerebellum planning and corrects movements
- Basal nuclei aiding in planning movement
- Corticospinal (direct) pathway
What are the effects of upper motor neuron destruction?
Spastic paralysis and exaggerated reflexes
What are the effects of lower motor neuron destruction?
Loss of reflex arc and flaccid paralysis
What brain areas are involved in language?
Cerebral cortex, Wernicke’s area, Broca’s area, basal nuclei, and visual and auditory cortex.
