Nervous System Flashcards
Organs of the Nervous System
- Brain and spinal cord
- Sensory receptors of sense organs (eyes, ears, etc.)
- Nerves connect nervous system with other systems (nerve is a bundle of axons).
- Spinal nerves and Cranial
nerves
- Spinal nerves and Cranial
Basic functions of nervous system
- Sensory function – senses certain changes (stimuli) both within (internal environment) and outside (external environment) the body
- Integrative function – analyses sensory information, stores some aspects, and makes decisions regarding appropriate behaviour
- Motor function – may respond to stimuli by initiating muscular contractions or glandular secretions.
Special Sensory Receptors
monitor smell, taste, vision, balance and hearing
Visceral Sensory Receptors
monitors internal organs
Somatic Sensory Receptors
monitor skeletal muscles, joints and skin surface
Central nervous system (CNS)
- Brain and spinal cord
- Divided into grey and white matter
- Supported by neural tissue (neurons and glia), CT and blood vessels
- Is protected by bone and meninges (CT)
Peripheral nervous system (PNS)
- Cranial and spinal nerves
- Nerves can have both sensory and motor axons
- Nerves are supported by glia, CT and blood
- Includes somatic nervous system (SNS) and autonomic nervous system (ANS)
- All neural tissue outside the CNS
- Delivers sensory information to CNS; delivers motor commands from the CNS
- Bundles of axons (nerve fibres carry this information)
- Consists of 12 pair of cranial nerves and 31 pair of spinal nerves.
- The cranial nerves carry
impulses between the brain,
head and neck with only 1
exception (vagus nerve) - The spinal nerves carry impulses
between the spinal cord, the
chest, abdomen and extremities
- The cranial nerves carry
Functions of the CNS
- Are to process and coordinate:
- sensory data: from inside and
outside body - motor commands: control
activities of peripheral organs
(via muscles, glands) - higher functions of brain:
intelligence, memory, learning,
emotion
- sensory data: from inside and
- CNS – information processed at conscious and subconscious levels
- CNS – integrates physiology and psychology
Example of CNS
E.g. in Thermoregulation
CNS in Thermoregulation
- Blood temperature is the stimulus
- The hypothalamus can respond to the change in temperature (outside
the set range) - The hypothalamus in response turns on:
- Heat loosing
- Heat gaining mechanisms
Afferent division
Brings information to the CNS
Efferent division
- Carries motor commands to muscles and glands
- Somatic nervous system provides voluntary control
- Autonomic nervous system provides involuntary control
PNS- Somatic nervous system
- Control skeletal muscle contractions
- Voluntary contraction – under
conscious control e.g. control over
arm to raise full glass of water to
your lips - Involuntary contractions –
controlled at subconscious level e.g. if you accidentally placing your
hand on hot stove you move it
away immediately - Automatic response is called a reflex
PNS- Autonomic nervous system
- ANS automatically regulates smooth muscle, cardiac muscle, glandular secretions, and adipose tissue at subconscious level
- Parasympathetic and sympathetic
division -> antagonistic effects- E.g. parasympathetic activity slows the heart rate;
- Sympathetic activity accelerates
the heart rate
Neurons
basic functional unit of the nervous system
* Specialised for intercellular communication
Functions of Neuroglia
- Survival and functioning of neurons
- Preserving the physical and biochemical structure of nervous tissue
- 70% of brain tumours are tumours of a glial cell
- Perform phagocytosis
- Provide nutrients to neurons
- Repairs tissue framework after injury
- Regulates the composition of the interstitial fluid surrounding neurons
General Anatomy Regions of a Neuron
- A large cell body
- Several short, branched dendrites
- Single, long axon
- Terminal branches of the axon called telodendria
The Cell Body of a Neutron
- Large, round nucleus – prominent nucleolus
- Cytoplasm is the perikaryon
- Cytoskeleton of the perikaryon contains neurofilaments and neurotubules
- Bundles or neurofilaments, called neurofibrils, extend into the dendrites and axon, providing internal support for them
Dendrites
- Extend and branch out from the cell body
- Play key roles in intracellular communication
- Highly branched, some studded with projections called dendritic spines (0.5 to 1μm long)
- These participate in synapses
- In the CNS, a neuron receives information from other neurons primarily at the dendritic spines, which may represent 80-90 percent of the neuron’s total surface area
Axons
- Long cytoplasmic process capable of propagating an electrical impulse known as an action potential
- Axoplasm – cytoplasm of the axon
- contains neurofibrils, neurotubules, small vesicles, lysosomes, mitochondria, and various enzymes
- Axolemma – plasma membrane of the axon
- surrounds the axoplasm
- in the CNS, the axolemma may
be exposed to interstitial fluid or
it may be covered by the cellular
processes of neuroglia
- Axon hillock – thickened region where the base (or initial segment) of the axon in a typical neuron joins the cell body
Axon Functions
- Axons create and pass electrical signals (AP) along their length. May be up to 1m long
- The end of the axon is called the synaptic terminal
- Chemicals are released from the synaptic terminal
- Nerves Communicate at a synapse
The synapse
- In the nervous system, messages move from one location to another in the form of action potentials along axons
- Transfer of message from one neuron to another takes place at a synapse- a specialised site where the neuron communicates with another cell
- Information passes from presynaptic neuron to postsynaptic neuron
- Synapses may also involve other types of postsynaptic cells
- e.g., the neuromuscular junction is a synapse in which the postsynaptic cell is a skeletal muscle fiber
- Axon terminal of presynaptic cell releases chemicals called neurotransmitters into the synaptic cleft
- Neurotransmitters are contained in synaptic vesicles
- Synaptic cleft separates presynaptic membrane from postsynaptic membrane
- Each axon terminal contains mitochondria and vesicles filled with neurotransmitter molecules
Types of Synapses
- Electrical
- Chemical
Telodendria
- Axon may branch along its length – producing side branches known as collaterals
- Collaterals enable a single neuron to communicate with several other cells
- The main axon trunk and any collaterals end in a series of find extensions called telodendria, or terminal branches
- End at axon terminals, or synaptic terminals– role in communication with another cell
Classification of Neurons by Structure
Anaxonic neuron
Bipolar neuron
Unipolar neuron
Multipolar neuron
Anaxonic Neuron
have more than two processes, and they may all be dendrites; axons are not obvious
Bipolar Neuron
have two processes separated by the cell body.
Unipolar Neuron
have a single elongated process, with the cell body located off to the side
Multipolar Neuron
have more than two processes; there is a single axon and multiple dendrites
Classification of Neurons By Function
Sensory neurons
Interneurons
Motor neurons
Motor neurons
bring nerve signals away from the brain and spinal cord
Sensory Neurons
- Also known as afferent neurons
- Form afferent division of the PNS
- bring nerve signals to the brain and spinal cord
Interneurons
bring nerve signals from one nerve cell to another within the brain and spinal cord -> make connections between sensory and motor neurons
Neural activities
- Resting potential
- Graded potential
- Action potential
- Synaptic activity
- Information processing
Satellite Cells
-Surround neuron cell bodies in ganglia
-Regulate O2, CO2, nutrient and neurotransmitter levels around neurons in ganglia
Schwann Cells
-Surround axons in PNS
-Are responsible for myelination of peripheral axons
-Participate in repair process after injury
Oligodendrocytes
-Myelinate CNS axons
-Provide structural framework
Astrocytes
-Maintain blood-brain barrier
-Provide structural support
-Regulate ion, nutrient and dissolved gas concentrations
-Absorb and recycle neurotransmitters
-Form scar tissue after injury
Microglia
-Removes cell debris, waste and pathogens by phagocytosis
Ependymal Cells
-Line ventricles (brain) and central canal (spinal cord)
-Assist in producing, circulating and monitoring of cerebrospinal fluid
CNS- Types of Neuroglia
- Ependymal cell
- Microglial cell
- Oligodendrocyte
- Astrocyte
PNS- Types of Neuroglia
- Satellite cells
- Schwann cells
Formation of myelin sheath in the PNS
- A myelinating Schwann cell
myelinates only one axon, (whereas an oligodendrocyte in the CNS
may myelinate several axons) - Non-myelinating Schwann cells can enclose segments of several unmyelinated axons
- A series of Schwann cells is required to enclose an axon along its entire length
Neural responses to injuries
- Fragmentation of axon and myelin occurs in distal stump.
- Schwann cells form cord, grown into cut and unite stumps. Macrophages engulf degenerating axn and myelin.
- Axon sends buds into network of schwann cells and then starts growing along cord of schwann cells.
- Axon continues to grow into distal stump and is enclosed by schwann cells.
Reflexes
quick, automatic responses triggered by specific stimuli;
* Regarded as fast, predictable, protective, automatic (subconscious) response to a
stimulus
* preserve homeostasis by making rapid adjustments in the function of organs or organ systems
Spinal reflexes
controlled in the spinal cord, they function without any input from the brain
* E.g., a reflex controlled in the spinal cord makes you drop a frying pan you didn’t realise was sizzling hot -> Before the information reaches your brain and you become aware of the pain, you’ve already released the pan
A Reflex Arc Includes:
- Sensory Receptor structure
- Sensory nerve cell
- Interneuron(s) (in most cases)
- Motor nerve cell
- Effector
The monosynaptic reflex
The simplest reflex arc.
A sensory neuron synapses directly on a motor neuron.
Transmission across a chemical synapse always involves a synaptic delay, but only one synapse, the delay between the stimulus and response is minimised.
Example of The monosynaptic reflex
Stretch flex
Example of a Stretch flex
Patellar reflex
Reflex Pathways
- Involve the central nervous system (brain and spinal cord)
- The peripheral nerves (cranial nerves, spinal nerves and sensory receptors)
- The sensory information is processed in the Central Nervous System (CNS)
- The CNS then directs the motor response
CNS – brain and spinal cord
Grey matter
of the brain and spinal cord is where nerve cell bodies are concentrated.
* Also the site of incoming signals (and therefore synapses)
* Grey because of cell body structures
* Where information from one neuron is passed onto another neuron
- this involves processing
* Decisions are made in the grey parts of the brain and spinal cord
* Mostly on the outside of brain tissue
* On the centre of the spinal cord
* Darker
White Matter
of the brain and spinal cord is where bundles of axons are found
* White areas of the brain are the
connections between one part of the brain and another
* White because of fatty tissue (myelin) in the glial cells that surround the axon
* White matter colour is due to the
glial cell membrane structure
* Where information is brought from one part of the CNS to another
-this involves pathways called tracts
Classifications of Reflexes
-By processing site
-By complexity of circuit
-By response
-By development
Reflexes by processing site
-Spinal Reflexes: processing in the spinal cord
-Cranial Reflexes: processing in the brain
Reflexes by complexity of circuit
-Monosynaptic: one synapse
-Polysynaptic: multiple synapses (two to several hundred)
Reflexes by response
-Visceral (Autonomic) Reflexes: control by actions of smooth and cardiac muscles and glands
-Somatic Reflexes: control skeletal muscle contractions and include superficial and stretch reflexes
Reflexes by development
-Innate Reflexes: genetically determined
-Acquired Reflexes: learned
