Nervous System Flashcards
What is the nervous systems function?
The Nervous system allows us to sense and respond to conditions inside and outside the body.
What germ layer does the nervous system develop from?
The nervous system develops from the ectoderm
What does the CNS consist of?
The Central Nervous System consists of the brain and spinal cord.
What does the PNS consist of?
The Peripheral Nervous System consists of cranial nerves, spinal nerves, and associated ganglia.
What is a cranial nerve and how many are there?
A cranial nerve connects the brain to organs mainly in the upper head / body.
There are 12 pairs of cranial nerves.
What are the spinal nerves and how many are there?
The spinal nerves connect the spinal cord to parts of the body below the head.
There are 31 pairs of spinal nerves.
What are the two subdivisions of the PNS?
The Peripheral nervous system consists of two subdivisions:
- Somatic Nervous System: Voluntary. Will carry impulses to skeletal muscles, tendons, and skin
- Autonomic Nervous System: Involuntary. Impulses are carried to cardiac muscle, smooth muscle, or glands.
What are the three subdivisions of the autonomic nervous system?
The three subdivisions of the autonomic nervous system are:
- sympathetic: Fight or Flight, energy generation. (increased heart rate, tense muscles, blood vessels constrict, all digestion stops)
- parasympathetic: Rest and Digest, calmness. (decreased heart rate, dilated blood vessels, digestion)
- Enteric: controls the secretory and motile functions of the digestive tract
What is a motor neuron?
Also known as efferent, a motor neuron relays signals from the brain or spinal cord to muscle or gland cells.
What is a sensory neuron?
Also known as afferent, a sensory neuron relays signals from the internal and external environment to the CNS.
What is the Pneumonic for Motor and Sensory neurons?
SAME
Sensory - afferent
Motor - efferent
What is a ganglion?
A ganglion is a mass of neuron cell bodies usually found outside the CNS
What is a Neuron composed of?
A neuron is the basic unit of nervous tissue, it is a nerve cell including cell body (soma), axon, and dendrites
What is the difference between an axon and a dendrite?
An axon conducts neural impulses away from the cell body (soma)
A dendrite conduct neural impulses toward the cell body (soma)
How many neurons are in the body?
There are over 100 billion neurons in the body.
How do neurons reproduce?
- THEY DON’T!
- They are so specialized that they are incapable of reproducing themselves.
- Replacing old neurons with new neurons would literally “erase” our memory away, thus there is no mitosis in these cells.
- There ability for regeneration is very poor.
Describe the nucleus and organelles of the neuron
The neuron has the following organelles:
- Nissl bodies ( A specialized neural cell organelle that is essentially a large complex of rough ER and ribosomes)
- mitochondria
- ribosomes
- golgi apparatus
- lysosomes
- The nucleus is large
What are nissl bodies?
Nissl bodies are specialized organelles in the neuron that are composed of large branching Rough ER and ribosomes.
Describe the brains relationship to glycogen
- Glycogen is stored in the brain, but not at the same levels as the liver or skeletal muscle.
- Glycogen is stored in specialized non-neuronal cells called astrocytes.
What are glial cells?
Glial cells surround neurons and provide support and protection for them. Glial cells represent the most abundant cell in the CNS. They include:
- Astrocytes
- Oligodendrocytes
- Schwann Cells
- Microglia
- Satellite cells,
- Ependymal cells
What is an Axon?
- An axon is an extension of a neuron that carries nerve impulses away from the cell body (soma) to target cells such as the nerve, muscle, or gland cells.
- No neuron has more than a single axon.
What is a Dendrite?
A dendrites are highly branched neuronal extensions that bring nerve impulses toward the cell body (soma)
Where are mitochondria located in the neuron?
Mitochondria are found scattered all over the cytoplasm of the cell body, axon, and dendrites, but it is most abundant at the axon terminals
What are axon terminals?
Axon terminals are the end of the axon where neurotransmitters get released into the synapse
What are astrocytes?
Astrocytes are star shaped cells found in the brain.
- most numerous glial cell
- regulate electrical impulses
- provide neurons with lactate for nutrients
- contain channels for K+ transport
- regulates blood flow
- takes part in neural repair
- stores glycogen
What are oligodendrocytes?
Oligodendrocytes make myelin in the CNS
What are schwann cells?
Schwann cells make myelin in the PNS
What is the blood brain barrier?
The blood brain barrier consists of high density endothelial cells that prevent the passage of pathogens, antibiotics, and chemicals into the brain.
- Some molecules such as CO2, O2, water, glucose, and amino acids can cross.
- Bottom line: It protects the brain from toxic substances and pathogens
What is multiple sclerosis?
Multiple Sclerosis is an auto-immune disease
- A part of the blood brain barrier breaks down allowing T-lymphocytes to cross over and attach the myelin sheath.
- It results in communication issues with your brain and the rest of the body.
What is epilepsy
Epilepsy is uncontrolled seizures.
- Also shown to be caused by failures of the blood brain barrier.
What happens when the sympathetic nervous system is stimulated?
When the sympathetic nervous system is stimulated it:
- Increases heart rate
- Increases blood pressure
- Increases respiration
- Increases blood flow to skeletal muscles
- Pupil Dilation
- Stimulates adrenal medulla (epinephrine and norepinephrine)
- Stimulates glycogenolysis
- Slows intestinal and stomach movements
- Salivary gland secretion decreases
- Decreases urine production
- Relaxes urinary bladder (takes away urge to pee)
- Fight or Flight
What happens when the parasympathetic nervous system is stimulated?
When the parasympathetic nervous system is stimulated:
- Decreases heart rate
- Decreases blood pressure
- Decreases blood flow to skeletal muscles
- Pupil constriction
- Stimulates intestinal and stomach movements
- Salivary gland secretions increase
- Increases urinary production
- Tenses urinary bladder (makes you want to pee)
- Rest and digest
What is the enteric nervous system?
The enteric nervous system is part of the autonomic nervous system.
- It extends the entire length of the alimentary tract (esophagus to anus)
- It controls the secretory and motile functions of the digestive tract
- Contains a large number of neurons (100 million), that’s more than the spinal cord.
- Sometimes dubbed the second brain, it can work independent of parasympathetic or sympathetic systems, or in tandem with them.
- Makes over 30 neurotransmitters
- 90% of our serotonin and a good percentage of our dopamine is made here.
What is the myelin sheath?
The Myelin sheath is a fatty substance surrounding some axons that increase the speed of impulse along the axon
- Electrically insulating
- needed for proper functioning
- made up of cholesterol, lipids, and about 20% proteins
- Made by schwann cells in the PNS
- Made by oligodendrocytes in the CNS
- Unmyelinated fibers have slower impulse speed
Where are myelinated axons found in the brain?
In the brain:
- Grey matter: consists of mainly unmyelinated axons
- White matter: consists of mainly myelinated axons
What is the axolemma
The axolemma is the cell membrane surrounding the axon.
What are the nodes of Ranvier?
The nodes of ranvier are gaps between adjacent schwann cells.
- At these nodes, the axolemma is especially permeable to Na+ and K+.
- These nodes are only present when the axon is myelinated
- Action potentials can jump between these nodes in what is called saltatory conduction.
What is saltatory conduction?
As the neural impulse travels down the axon, it starts to lose some of its strength. At the nodes of ranvier, the impulse of the axon triggers the release of more action potential effectively boosting the signal of the impulse. This perpetual boosting of the signal through the myelinated axon increases the speed dramatically vs an unmyelinated axon.
What is the difference in speed between a myelinated and unmyelinated neuron?
- A Myelinated neuron can transmit an impulse at 120 m/s
- An unmyelinated neuron can transmit an impulse at less than 1 m/s
What is the cerebrum?
The cerebrum is:
- The largest part of the mature brain (80%)
- Consists of two hemispheres connected by a deep bridge of nerve fibers called the corpus callosum
- Each hemisphere is surrounded by an outer covering of grey matter called the cerebral cortex
- The inner portion of the cerebrum consists of white myelinated matter that acts as the communication portion of the brain.
What is the corpus callosum?
The corpus callosum is a deep bridge of nerve fibers that connects the two hemispheres of the brain.
- It is composed of white matter for quick communication between hemispheres
- It is the largest white matter structure in the brain
What is the cerebral cortex?
The cerebral cortex is the outer covering of grey matter that surrounds the cerebrum.
- Cortex means outermost layer. Cerebral means of the cerebrum
What does the brain’s gray matter consist of?
The gray matter consists of:
- Unmyelinated portions of axons
- cell bodies
- glial cells
- dendrites
Most of the brain’s neuronal cell bodies are here.
They gray matter includes regions of the brain involved with seeing, hearing, memory, speech, emotion, and decision making, among others
What does the brain do to pack more gray matter in a smaller space?
The cortex is wrinkled to allow more gray matter to fit into the small amount of space in our skull. The wrinkles are called covolutions or gyri, which are separated into two categories:
- Shallow groove: sulcus
- Deep groove: Fissure