NERVOUS SYSTEM Flashcards
Nervous system
Body’s command centre originating from the brain and controlling thoughts, movement and automatic responses
Central nervous system
Composed of the brain and spinal cord. The brain is contained within the cranial cavity of the skull, and the spinal cord is contained within the vertebral cavity of the vertebral column
Peripheral nervous system
Everything outside of the central nervous system; made up of nerves that branch off from the spinal cord and extend to all parts of body (ganglion & nerves)
Cerebrum (CNS) divisions (2)
Cerebral cortex, basal nuclei
Diencephalon (CNS) divisions (4)
Thalamus, hypothalamus, epithalamus, subthalamus
Brain stem (CNS) divisions (3)
Midbrain, pons, medulla
Division of CNS with no extensions on the slide lol iykyk
Cerebellum
Ganglia (PNS) divisions (2)
Sensory ganglia, autonomic ganglia
Nerves (PNS) divisions (2)
Cranial nerves, spinal nerves
Division of PNS with no extensions iykyk
Enteric Nervous System
Nervous tissue
The nervous tissue in the CNS and PNS contains two basic cell types; neurons and glial cells
Neurons
Involved in communicative function of the nervous system
Glial cells
Provides framework of tissues that supports the neurons and their activities
Neuron structure
Soma/cell body, dendrites, axon
Soma/cell body
Contains nucleus, has most cytoplasm, organelles and connects to dendrites, which bring information into the neuron, and the axon
Dendrites
Branches off cell body and appear as thin extensions. They receive most of the input from other neurons and carry the signals to cell body
Axon
Extends from the cell body and is the process that connects the neuron with its target. They carry electrical impulses that are the means of communication within the brain and between the brain and the rest of the body
Extensions on neurons
Called processes
Polarity of neurons
Neurons are polar because information flows in one direction
Axon hillock
Special region where the axon emerges from the soma where the cell tapers
Myelin sheath
Lipids insulating the axon that facilitates the transmission of electrical signals across axon (phospholipids of the glial cell membrane)
Nodes of ranvier
Gaps on the axon that are NOT insulated by myelin. Contains sodium and potassium ion channels allowing the action potentials to travel down the axon quickly jumping from one node to the next
Axon segment
Length of axon between each gap that is wrapped in myelin
Axon terminal
End of an axon where there are usually several branches extending towards the target cell
Synapse
End bulbs of the axon terminal that connect neurons and help transmit information from one neuron to another
Gray matter
Outer cortex of brain and region of nervous tissue with cell bodies and dendrites. Not necessarily gray as it can be pinkish because of blood content or even tan depending on how long the tissue has been preserved
White matter
Region of nervous tissue that contains axons insulated by a lipid rich substance called myelin sheath that makes it appear white
Colors of white and gray matter
Colors in white and gray matter are what would be seen in fresh or unstained tissue
Group of neuron cell body (gray matter) terminology CNS/PNS
Group of neuron cell bodies in the CNS is referred to as the nucleus. In the PNS, it is referred to as a ganglion
Bundle of axons (white matter) terminology CNS/PNS
A bundle of axons, or fibers found in the CNS is called a tract. In the PNS, it is called a nerve
Give an example of the different uses of terminology regarding the location of bundle of axons
Axons of the eye are called optic nerves as they LEAVE the eye, but when they are inside the cranium, they are referred to as the optic tract
Basic functions of the nervous system (3)
Sensation –> integration –> response
Divisions of the control of the body (2)
Somatic or autonomic
Sensation
Nervous system receives information from the environment through a stimulus (sensation) and generates appropriate responses (eg. Vision, audition, olfaction, propioception)
Integration
Stimuli is compared with, or integrated with other memories of previous stimuli information and becomes processed (at brain and spinal cord)
Response
Integration combines sensory perceptions and higher cognitive functions such as memories, learning, and emotion to produce a response
2 divisions of a response:
- Somatic nervous system (voluntary response)
- Autonomic nervous system (involuntary response)
- Both are divisions of the PNS
Somatic nervous system
Controls conscious perception and voluntary motor responses; contraction of skeletal muscles
Autonomic nervous system
Responsible for involuntary control of the organ system of the body like homeostasis; contraction of smooth muscles, regulation of cardiac muscle, activation of glands –> Sympathetic system/parasympathetic system
Sympathetic system
Fight or flight response
Parasympathetic system
Rest and digest response
Enteric nervous system
Large part of the PNS and is not dependant on CNS. It is responsible for controlling the smooth muscle and glandular tissue in digestive system
Why is it sometimes valid to consider the enteric system to be a part of the autonomic nervous system
Because the neural structures that make up the enteric system are a component of the autonomic output that regulates digestion
Brain (CNS) (3):
- Perception and processing of sensory stimuli (somatic/autonomic)
- Execution of voluntary motor responses (somatic)
- Regulation of homeostatic mechanism (autonomic)
Spinal cord (CNS) (2):
- Initiation of reflexes from ventral horn (somatic) and lateral horn (autonomic) gray matter
- Pathways for sensory and motor functions between periphery and brain (somatic/autonomic)
Nerves (PNS):
- Fibers of sensory and motor neurons (somatic/autonomic)
Ganglia (PNS) (2):
- Receive and process sensory stimuli.
- Relay motor responses in the autonomic nervous system
Digestive tract (ENS):
- Responsible for autonomous functions and can operate independantly of the brain and spinal cord
Identifying types of neurons (3):
- Shape of neuron and the number of processes attached to cell body
- The names for the neurons are based on the cell’s polarity
- Can be classified on where they are found, who found them, what they do, or the types of chemicals used to communicate
Glial cells (neuroglia/glia)
Other type of cell found in nervous tissue that are supporting cells and their functions are directed at helping neurons complete their functions for communication; 6 types, 4 found in CNS and 2 found in PNS
6 types of glial cells:
- Astrocyte (CNS): Support
- Oligodendrocyte (CNS): Insulation, myelination
- Microglia (CNS): Immune surveillance, phagocytosis
- Ependymal cell (CNS): Create cerebrospinal fluid
- Satellite cell (PNS): Support
- Schwann cell (PNS): Insulation, myelination
Brain function
Person’s conscious experiences, the regulation of homeostasis, and coordination of reflexes are al based on neural activity in the brain
Adult brain regions (4):
- Cerebrum
- Diencephalon
- Brain stem
- Cerebellum
Cerebrum
Makes up most of the brain and is composed of two halves (right and left cerebral hemispheres) and a continuous, wrinkled and thin layer of grey matter that wraps both hemispheres and the cerebral cortex. Functions in memory, emotion, consciousness
Cerebral cortex divisions
Frontal lobe, parietal lobe, temporal lobe, occipital lobe
Gyrus
Ridge of one of the wrinkles on the cerebral cortex
Sulcus
Groove between the two gyri of cerebral cortex
Why is the pattern of the folds of tissues important on the brain
Because it indicates specific regions of the cerebral cortex
Basal nuclei (3):
- Found beneath the cerebral cortex and augment cortical processes
- Some basal nuclei in forebrain serve as primary location for acetylcholine production
- Some basal nuclei control initiation of movement (eg. Keeps an urge to jump or scream during class)
Acetylcholine production
Modulates overall activity of cortex and leads to greater attention to sensory stimuli
Alzheimer’s disease
Associated with a loss of neurons in the cholinergic basal forebrain nuclei leading to memory loss, loss of control thought and language
Diencephalon
Connection between the cerebrum and almost all of the nervous system (except for olfaction - sense of smell). The rest of the brain, spinal cord, PNS all send information to the cerebrum through the diencephalon and output from the cerebrum passes through diencephalon
2 major regions of the diencephalon:
- Thalamus: Collection of nuclei that process and relay information between cerebral cortex and the PNS, spinal cord, or brain
- Hypothalamus: Collection of nuclei inferior and slightly anterior to the thalamus that are involved in regulating homeostasis and being in charge of the ANS and the endocrine system
Epithalamus
Contains pineal gland
Subthalamus
Includes subthalamus nucleus, one of the basal nuclei
Brain stem (4):
- The midbrain and the hindbrain (pons and medulla)
- Emerges from ventral surface of forebrain as a tapering cone that connects brain and spinal cord
- Cranial nerves connect through the brain stem and provide brain with sensory input and motor output associated with head and neck
- The major ascending and descending pathways between the spinal cord and brain (specifically cerebrum) pass through brain stem
Midbrain
Includes four bumps known as the cuniculi
Inferior cuniculus
Part of auditory brain stem pathway
Superior cuniculus
Combines sensory information about visual space, auditory space and somatosensory space
Pons
Main connection between the brain stem and cerebellum
Medulla oblongata
Continuation of gray matter of the midbrain and pons. It controls the rate and force of heart contraction, diameter of blood vessels, and the rate and depth of breathing
Reticular formation
Diffuse region of gray matter that runs through the medulla and pons associated with sleep and wakefulness
Spinal cord
Tube structure specialized into certain regions that correspond to the regions of the vertebra column
Regions of spinal cord
Consists of a cervical, thoracic, lumbar, and sacral regions where each region corresponds to the level at which spinal nerves pass through the intervertebral foramina
Gray matter of spinal cord
Has a shape of capital H and is subdivided into regions referred to as horns
Posterior horns
Region of gray matter in spinal cord responsible for sensory processing
Anterior horns
Region of gray matter in spinal cord that sends out motor signals to skeletal muscles
Lateral horns
Special region of spinal cord only found in thoracic, sacral, upper lumbar responsible for ANS
White matter of spinal cord
White matter of spinal cord separated into columns
Ascending tracts
Ascending tracks of nervous system fibers in the columns carry sensory information up to the brain
Descending tracts
Descending tracks of nervous system in columns carry motor commands from the brain
Meninges
Membranes composed of connective tissues that cover the outer surface of the CNS. It helps to protect the brain
3 types of meninges
Dura mater, arachnoid mater, pia mater
Dura mater
Thick fibrous layer and a strong protective sheath over the entire brain and spinal cord
Arachnoid mater
Membrane of thin fibrous tissue that forms a loose sac around the CNS. Arachnoid trabeculae, a thin filamentous mesh layer found beneath the arachnoid mater
Pia mater
A thin fibrous membrane that follows the convolutions of gyri and sulci in cerebral cortex and fits into other grooves and indentations. It is found directly adjacent to the surface of the CNS
Cerebrospinal fluid
Continuous with the interstitial fluid and circulates throughout and around the CNS to remove metabolic wastes from the interstitial fluid. It is a clear solution with limited amount of solutes and acts as a liquid cushion for the brain and spinal cord
Ventricles of brain
Open spaces within the brain where the CSF circulates to emerge into the subarachnoid space and reabsorbed into the blood
First and second ventricles
Lateral ventricles deep within cerebrum
Third ventricle
Space between left and right sides of diencephalon
Fourth ventricle
Space between the cerebellum and the pons/medulla. Cerebral aqueduct –> third ventricle –> fourth ventricle
Choroid plexuses
Found in all four ventricles and assist in producing CSF
CSF pathway in lateral ventricles
CSF flows into the third ventricle, then the cerebral aqueduct and then into the fourth ventricle
CSF pathway in fourth ventricle
CSSF continues down the central canal of spinal cord
How does CSF flow through CNS overall
Median and lateral structures open from the ventricular spaces to the subarachnoid space which allows the CSF to flow all through the CNS
Peripheral nervous system
Not as contained as the CNS because it is defined as everything that is not the CNS and contains nerves and ganglia
Ganglion
Group of neuron cell bodies in the PNS categorized as either sensory or autonomic ganglia
Dorsal root ganglion
emerges from the dorsal root of the spinal nerves. They carry sensory messages from various receptors (i.e., pain and temperature) at the periphery towards the central nervous system for a response.
Nerves (4):
- Bundles of axons in the PNS
- Composed of more than just nervous tissue
- Contains connective tissue invested in their structure, as well as blood vessels supplying the tissues with nourishment
- Associated with the region of the CNS to which they are connected (eg. Cranial nerves or spinal nerves)
Cranial nerves
12 pairs of cranial nerves primarily responsible for the sensory and motor functions of the heart and neck
Vagus nerve
One of the cranial nerves that targets organs in the thoracic and abdominal cavities as part of the parasympathetic nervous system
12 cranial nerves:
- Olfactory: Smell
- Optic: Vision
- Oculomotor: Eye movement and pupil reflex
- Trigeminal: Face sensation and chewing
- Facial: Face movement and taste
- Glossopharyngeal: Throat sensation, taste, and swallowing
- Accessory: Neck movement
- Trochlear: Eye movement
- Abducens: Eye movement
- Vestibulocochlear: Hearing and balance
- Vagus: Movement, sensation and abdominal organs
- Hypoglossal: Movement, sensation and abdominal organs
Spinal nerve
31 pairs of spinal nerves that are combined sensory and motor axons that separate into two nerve roots. Each of the sensory axons enter the spinal cord as the dorsal nerve root and each of the motor fibers (somatic/autonomic) emerge as the ventral nerve root
Somatic nervous system
unctional division within the peripheral nervous system responsible for conscious perception of the environment and voluntary responses to that perception by skeletal muscles n the PNS sensory neurons receive input and neurons in the CNS produce motor responses
Patellar reflex
Example of a stretch reflex where the nervous system responds to the stretching of a muscle with the contraction of that same muscle
a kicking-like motion produced by the extension of the knee joint upon the ipsilateral stimulation of the patellar tendon
Withdrawl reflex
Response generated to a painful stimulus where the nervous system responds to the painful stimulus by contracting a muscle that pulls that body part away
Stretch reflex (3):
- The quadriceps muscle stretches and stimulates sensory neurons to generate a nerve impulse
- The impulse travels through the dorsal root ganglion to the spinal cord where a motor neuron is stimulated in the ventral horn
- The motor neuron sends an impulse along its axon to the quadriceps causing its contraction and the leg to kick
Withdrawl reflex (3):
- Sensory receptors in skin sense extreme temperature and the early signs of tissue damage, generating a nerve impulse
- Impulse travels through the dorsal root ganglion to the spinal cord where a motor neuron is stimulated in ventral horn
- Motor neuron sends an impulse along its axon and reaches a skeletal muscle causing its contraction and removal of the body part from painful stimulus
Autonomic nervous system
Two divisions (sympathetic division; fight or flight, and parasympathetic division; rest and digest) controls cardiac, smooth muscles contraction, and glandular tissue associated with involuntary responses like homeostasis
Ways that effector organs can be activated during fight or flight - sympathetic nervous system (5):
- Increase heart rate, respiratory rate, musculoskeletal systems
- Secretion of sweat glands.
- Slowing down or stopping digestion so blood not absorbing nutrients
- More oxygen delivered to skeletal muscle
Thoracolumbar system SYMPATHETIC NERVOUS SYSTEM
stimulating fight-or-flight responses in the body by influences organ systems through connections that emerge from the thoracic and upper lumbar spinal cord
Sympathetic chain ganglia SYMPATHETIC NERVOUS SYSTEM
Deliver information to the body about stress and impending danger, and are responsible for the familiar fight-or-flight response.They appear as a series of clusters of neurons linked by axonal bridges
Preganglionic fiber SYMPATHETIC NERVOUS SYSTEM
First set of nerves fibres originating from CNS typically from brain stem or spinal cord and extending to ganglia. Deliver messages from CNS to ganglia. long and myelinated
Postganglionic fiber SYMPATHETIC NERVOUS SYSTEM
Second set nerve fibres extending from ganglia to target such as tissues or organs. Typically short and unmyelinated
Craniosacral system PARASYMPATHETIC NERVOUS SYSTEM
Parasympathetic division referred to as the craniosacral system because the preganglionic neurons are located in the nuclei of the brain stem and the lateral horn of the sacral spinal cord
Preganglionic fibers in cranial region and sacral region
Cranial region travel in cranial nerves and sacral region travels in spinal nerves
Signalling in the ANS (4):
- Where an autonomic neuron connects with a target, there is a synapse
- All preganglionic fibers and postganglionic parasympathetic fibers release acetylcholine
- The electrical signal of the action potential causes the release of a signaling molecule which will bind to receptor proteins on the target cell
- Synapses of the autonomic system are classified as either cholinergic, meaning that acetylcholine is released, or adrenergic meaning that norepinephrine is released
Cholinergic
Acetylcholine released by synapse
Adrenergic
Norepinephrine released by synapse
2 broad signalling molecules
Neurotransmitters can be released at synapses or hormones can be released into bloodstream
Ions
Most cells in the body make use of ions (charged particles) to build up a charge across cell membrane but it cannot be moved easily without assistance
Transmembrane channel proteins
Proteins that assist the movement of ions across membrane
What is needed to generate a transmembrane potential and action potential
Several passive channel proteins as well as active protein pumps
Ion channels
Pores that allow a specific charged particles to cross membrane in response to an existing concentration gradient
Sodium potassium pump
Moves sodium ions (Na+) out of a cell and potassium ions (K+) into a cell. It requires ATP energy to move these ions against their concentration gradient
Types of channels (3):
- Ion channels do not always freely allow ions to diffuse across membrane
- Some are opened by certain cellular events, meaning the channels are gated
- Eg. Ligand-gated, mechanically gated, voltage-gated and leakage channels
Ligand gated channels
Neurotransmitter acetylcholine binds to specific location on extracellular surface of channel protein and the pore opens to allow select ions (sodium, calcium and potassium cations)
Mechanically gated channel
Occurs when there is a mechanical change in the surrounding tissue such as pressure or touch and the channel is physically opened
Voltage gated channels
Opens when the transmembrane voltage changes around them and the amino acids in the structure of protein are sensitive to charge and causes pores to open to selected ions
Leakage channels
Randomly gated. There is no actual event that opens the channel so it is an intrinsic rate of switching between open and closed states
Potential
Distribution of charge across cell membrane in millivolts where the inside of the cell is compared to the outside. For a potential of -70mV, the inside is 70mV more negative than the outside
In the cell at rest… (4):
- The concentration of Na+ outside the cell ten times greater than inside
- Concentration of K+ inside is greater than outside
- Cytosol contains a large amount of phosphate anions and negatively charged proteins
- Distribution of ions causes a measured difference of -70mV called the resting membrane potential
Resting potential
Potential difference across the membrane of axon when it is not conducting an impulse
Voltage across membrane of axon resting
-70mV
Reason of negative polarity of resting
Due to presence of large organic negative ions (proteins) in axoplasm
Na and K concentrations at resting
More Na ions on the outside of axon compared to inside and more K ions on the inside compared to outside
How is the uneven distribution of Na and K maintained by
Active transport across Na+/K+ pump which operate whenever the neuron is not conducting an impulse
Action potential
When nerve impulse is generated and a change in voltage occur
Depolarization
When during UPSWING (-65mV to +30mV) the membrane becomes permeable due to Na channels opening and Na ions move from outside to inside of axon. It is called depolarization because the inside of axon becomes positive
Repolarization
When during DOWNSWING (+30mV to -70mV) due to K channels opening and K moves inside axon. It is called repolarization because the inside of axon becomes negative again
Refractory period
In between nerve impulses and transmissions. Causes inside of cell to become more negative than resting because of channels being inactive and cause cell to become less responsive to stimulus
Step 1 of nerve impulse conduction/propagation:
Sodium moves in; Sodium channels open and Na+ ions diffuse INTO axon
Step 2 of nerve impulse conduction/propagation
Depolarization; inside of axon of specific region is now positive
Step 3 of nerve impulse conduction/propagation
Na+ channels close and K+ opens; potassium channels open and K+ ions diffuse out of axon
Step 4 of nerve impulse conduction/propagation
Repolarization; Movement of K+ ions counters depolarization. The voltage difference across membrane returns to resting potential
Step 5 of nerve impulse conduction/propagation
Recovery period; Na+ and K+ actively transported back across membrane until concentrations are equally distributed as before impulse was sent (ATP STAGE USING CARRIER PROTEINS)
Step 6 of nerve impulse conduction/propagation
Depolarization of adjacent part of axon; Sodium channels open and Na+ ions diffuse into axon
Which stage uses ATP and why
Step 5 (recovery period) uses ATP for carrier proteins
What initiates the action potential by causing Na+ channels to open (4):
- Tigand gated Na+ channel: open due to NT binding
- Mechanically gated Na+ channel: open when physical stimulus affects sensory receptor
- Voltage gated Na+ channel: open once potential has risen to -55mV (threshold)
- Any depolarization that does not change the membrane potential to -55mV or higher will not reach threshold and thus will not result in an action potential
Two gates of the voltage gated Na+ channels
Activation gate (opens when the membrane potential crosses -55mV) and inactivation gate (closes after specific period of time)
Two types of synapse
Chemical; a chemical signal (NT eg. Neuromuscular junction) released from 1 cell and affects other, or electrical; direct connection between 2 cells so that ions can pass directly from one cell to next
Synapse characteristics (6):
- Presynaptic element
- NT
- Synaptic cleft
- Receptor proteins
- Postsynaptic element
- NT elimination
Sequence of events during synapse (8):
- Nerve impulse travels along axon and reaches synaptic ending
- Ca+ flows into ending through channel proteins
- Ca+ ions cause contractile proteins to pull out synaptic vessels to inner surface of presynaptic membrane
- Vesicles fuse with presynaptic end and realease NT
- NT diffuse across synaptic cleft to receptor on synaptic membrane
- NT binds to receptor that open ion channel
- Ion flux change voltage and move membrane voltage closer to threshold
- NT is degraded
4 main categories of NT systems:
- Amino acids
- Biogenic amines
- Cholinergenic system
- Neuropeptides
Amino acids
Single molecule building blocks of proteins (eg. Glutamate, GABA, glycine)
Glutamate
Main excitatory NT
GABA
Main inhibitory NT of brain
Glycine
Inhibitory NT of spinal cord
Biogenic amine
Enzymatically made from amino acids (eg. Dopamine, norepinephrine, serotonin)
Dopamine
Wanting, motivation, motor control
Norepinephrine
Wakefulness, sympathetic response
Serotonin
Satisfaction, arousal
Cholinergenic system
Based on the NT acetylcholine
Acetylcholine
Muscle contraction and memory
Neuropeptides
Molecules made up of chains of amino acids connected by peptide bonds (eg. Met-enkephalin, beta endorphin)
Endorphins
Have analgesic (pain reduction) and pleasure inducing effects
