Lec 1- Intro to the Nervous System Flashcards
PNS is composed of:
Nerve fibres and ganglia (collections of nerve cell bodies)
What is Sensory / Afferent?
Component of the nervous system that conveys information from sensory organs and receptors in the Peripheral Nervous System (PNS) to the Central Nervous System (CNS) for processing and perception.
What is Motor / Efferent?
Responsible for transmitting commands from the Central Nervous System (CNS), which includes the brain and spinal cord, to the Peripheral Nervous System (PNS) to initiate muscle contractions and other bodily responses.
Is the boundary between sensory and motor ambiguous in the PNS and most of the spinal cord?
No, the boundary between sensory and motor functions is not ambiguous in the PNS and most of the spinal cord. In these areas, afferent (sensory) and efferent (motor) signals travel in opposite directions along distinct fibers, making their separation clear.
Somatic System
Described as being associated with conscious and voluntary actions, however its not strictly true as many muscular actions are not conscious
What is the target of all efferent output in the somatic system?
All efferent output in the somatic system goes to skeletal muscles.
Autonomic system
Usually described as being unconscious and involuntary.
Where does the efferent output of the autonomic system go?
The efferent output of the autonomic system goes to cardiac muscles, smooth muscles, and glands.
What are the sub-components of the autonomic system?
The autonomic system is divided into three sub-components: sympathetic, parasympathetic, and enteric.
Sympathetic Nervous System
Generally associated with rapid responses
“Fight or flight”
- Not all sympathetic functions are emotionally charged in this way
Parasympathetic Nervous System
generally associated with slower responses and is often described as “rest and digest”?
How do the parasympathetic and sympathetic nervous systems typically interact with the same structures in the body?
They often work in opposite ways, creating a push/pull relationship. For example, parasympathetic activity decreases heart rate and constricts pupils, while sympathetic activity does the opposite.
Is the interaction between the parasympathetic and sympathetic systems antagonistic or complementary?
It is complementary rather than antagonistic, as both systems work together to maintain balance and regulation in the body.
What is the general role of the parasympathetic and sympathetic systems in regulating each other?
In general, these systems provide negative feedback regulation to actively produce homeostasis in the body.
Where is the enteric nervous system located?
The enteric nervous system is entirely housed within the digestive tract.
Why do some argue that the enteric nervous system is not really part of the autonomic system?
Some argue that the enteric nervous system is not truly part of the autonomic system because it can function effectively even if surgically separated from the sympathetic and parasympathetic systems.
What does “Rostral” mean in anatomical terms?
Rostral means forward or toward the front of an organism.
What does rostral mean in the brain?
In the brain, it refers to structures closer to the front or anterior part of the brain
What is the definition of “Caudal” in anatomy?
Caudal means backward or toward the tail of an organism.
What does rostral mean in the spinal cord?
It describes structures closer to the head or cranial end.
What does caudal mean in the brain?
.In the context of the brain, it refers to structures closer to the back or posterior part of the brain.
What does caudal mean in the spine?
In the spinal cord, it is used to describe structures closer to the tail or caudal end.
What does “Dorsal” mean in anatomical terms, and where is it used differently?
Dorsal means up or toward the back of an organism. In the brain, it refers to structures located toward the top or superior part of the brain. However, in the spinal cord, it describes structures located toward the back or posterior part of the spinal cord.
What is the anatomical definition of “Ventral” and how does it vary in the brain and spinal cord?
Ventral means down or toward the belly of an organism. In the brain, it refers to structures located toward the bottom or inferior part of the brain. In the spinal cord, it describes structures located toward the front or anterior part of the spinal cord.
What is the primary function of dendrites in a neuron?
Dendrites receive (most) incoming signals from other neurons.
What is the role of axons in a neuron?
Axons send signals away from the soma (cell body) to transmit information to other neurons.
What is found at the end of axons, where communication with other neurons occurs?
At the end of axons, there are synapses, where signals are transmitted to other neurons.
What happens when neurotransmitter molecules are released from the axon?
Neurotransmitter molecules are released from the axon and bound to receptors on the dendrites (or soma) of other neurons, facilitating communication.
What is the purpose of myelin sheathes in neurons?
Myelin sheathes increase the fidelity and speed of signal transmission along axons.
What happens when there is no myelin sheath around an axon?
Without a myelin sheath, signals can disperse out of the axon, leading to less efficient transmission.
What distinguishes principal or projection neurons?
Principal or projection neurons have long axons that extend beyond their immediate structure and terminate elsewhere, allowing for long-distance communication.
What characterizes intrinsic or interneurons?
Intrinsic or interneurons have shorter axons, which are primarily used for local communication within a specific region of the nervous system.
Why are areas with many grouped axons of projection neurons called “white matter” in living tissue?
White matter in living tissue appears white because it consists mainly of myelinated axons
What characterizes areas with many somas in the nervous system, leading to them being called “grey matter”?
Grey matter in the nervous system is characterized by regions with many cell bodies (somas)
How is the arrangement of white matter and grey matter typically seen in the spinal cord?
In the spinal cord, white matter (outside) surrounds grey matter.
Is the arrangement of white matter and grey matter the same throughout the entire nervous system?
No, the arrangement varies. In the upper brain, the reverse is generally true, where grey matter surrounds white matter (outside).
White matter is associated with:
long-distance information transmission.
How does white matter appear in stained pictures compared to grey matter?
White matter typically appears darker than grey matter in stained pictures due to differences in staining properties.
Grey matter is associated with:
local information processing
What is the grey matter at the surface of the brain often referred to as?
The grey matter at the surface of the brain is called the cortex or neocortex.
Why is it called the “neocortex”?
It is termed “neocortex” because it is evolutionarily younger than the rest of the brain, reflecting its more recent development in evolutionary history.
How does the amount of cortex vary across different species?
There is much more cortex in mammals than in reptiles, more in primates than in other mammals, and even more in humans compared to other primates.
How is brain surface area related to its level of wrinkliness?
Wrinkly brains tend to have more surface area due to the folding of the cortex.
What are the inward wrinkles on the brain’s surface called, and what are the outward wrinkles called?
The inward wrinkles are called sulci or sulcus, and the outward wrinkles are called gyri or gyrus.
What are the five main regions of the vertebral column?
The five main regions of the vertebral column are cervical (neck), thoracic (ribcage), lumbar (lower back), sacral, and coccygeal.
What is the role of the spinal cord within the vertebral column?
It serves as the primary pathway for transmitting sensory and motor signals between the body and the brain.
Horn (Dorsal/posterior, ventral/anterior, lateral)
Areas within spinal grey matter, typically seen in cross section
Columns (Dorsal/posterior, ventral/anterior, lateral, ventrolateral/anterolateral)
long connections up and down spine, within spinal white matter
Roots (Dorsal/posterior, ventral/anterior)
beginnings of the PNS and spinal nerves - outside the spine
What type of connections are typically found in the dorsal or posterior horn of the spinal cord?
The dorsal or posterior horn of the spinal cord contains afferent connections, which are responsible for receiving incoming sensory information.
What type of connections are located in the ventral or anterior horn of the spinal cord?
The ventral or anterior horn of the spinal cord contains somatic efferent connections, which transmit signals to skeletal muscles for motor control.
What type of connections are present in the lateral horn of the spinal cord?
The lateral horn of the spinal cord contains sympathetic efferent connections, which control functions such as cardiac, smooth muscle, or glandular activity.
Are there lateral horns in all regions of the spinal cord?
No, there are no lateral horns in the cervical or lower lumbar junctions of the spinal cord, meaning there are no sympathetic efferent connections in these regions.
What are spinal nerves composed of?
Spinal nerves are bundles of neurons that contain both afferent (sensory) and efferent (motor) fibers.
What are the main components of a spinal nerve?
A spinal nerve consists of ventral and dorsal roots, dorsal root ganglia (also known as spinal ganglia), and four rami (branches).
Dorsal Ramus:
The dorsal ramus is a branch of a spinal nerve that carries sensory and motor signals to and from the muscles and skin of the back.
Ventral Ramus
The ventral ramus is a branch of a spinal nerve responsible for carrying signals to and from the muscles and structures on the front and sides of the body.
White Ramus
A short myelinated nerve fiber that connects the spinal nerve to the sympathetic ganglia in the autonomic nervous system.
Grey Ramus
Unmyelinated nerve fiber that carries post-ganglionic sympathetic fibers back from the sympathetic ganglia to the spinal nerve.
Where are the cell bodies of sensory neurons located?
Sensory neurons have cell bodies in the dorsal root ganglion, which is located outside the spine.
Are there synapses in the dorsal root ganglia?
No, there are no synapses in the dorsal root ganglia
What are the three types of axonal projections from dorsal root ganglia into the spine?
1)Rostrally to the brain (majority of connections).
T2) To an interneuron in the dorsal horn, which projects to a motoneuron in the ventral horn, which, in turn, projects to skeletal muscle (forming a three-neuron reflex arc).
3) Directly to a motoneuron in the ventral horn, which projects to skeletal muscle (forming a two-neuron reflex arc).
How do somatic efferent projections leave the ventral horn?
Somatic efferent projections leave the ventral horn through the ventral root and eventually synapse directly on skeletal muscles.
What is the path taken by sympathetic efferent projections as they leave the lateral horn?
Sympathetic efferent projections leave the lateral horn via the ventral or anterior root and curve down the white ramus.
What are the initial sympathetic neurons that leave the CNS called?
The initial sympathetic neurons that leave the CNS are termed pre-ganglionic neurons. Their axons, known as pre-ganglionic fibers, are myelinated
Where do pre-ganglionic sympathetic neurons usually connect with other neurons?
Pre-ganglionic sympathetic neurons usually connect with post-ganglionic neurons in groups of nerve cell clusters called sympathetic ganglia, which can be found either close to the spine or a bit farther away in collateral ganglia.
What type of axons do post-ganglionic sympathetic neurons have, and what do they project to?
Post-ganglionic sympathetic neurons have unmyelinated axons (post-ganglionic fibers) that project to smooth muscles, cardiac muscles, and glands, either through the gray ramus that rejoins the spinal nerve or through independent connections
Efferent spinal connections involve two main types of innervation:
1) Autonomic Innervation: Controls involuntary functions such as heart rate, digestion, and glandular activity.
2) Somatic Motor Innervation: Efferent pathways that control voluntary muscle movements.
