Nervous System Flashcards
Where is the brain located and where does it lead to?
The brain is encased in the top of the skull
The base of the brain leads down to the spinal cord
What is the skull supported by?
The skull is supported by the spinal column, which is supported by the shoulders
What are the 4 regions and organisations of the brain?
- Cerebral hemisphere
- Diencephalon (thalamus, hypothalamus)
- Brain stem
- Cerebellum
Draw the organisation of the four regions of the brain
See lecture notes
Describe the ventricles of the brain
Hollow ventricular chambers, filled with cerebrospinal fluid and lined with ependymal cells which is a type of neuralgia
The human brain has 4 ventricles
- two lateral ventricles
- a third ventricle in the diencephalon region
- in the brain stem
Discuss the structures of the cerebral hemispheres
They make up 83% of total brain mass
The surface of the cerebral hemispheres are covered in ridges called gyri (singular gyrus) and grooves called sulci (singular sulcus)
Some sulci are used to divide the brain into anatomical regions termed lobes
Name the lobes of the brain
Frontal Parietal Temporal Occipital Cerebellum
Draw the structure of the brain and label the lobes
See lecture notes
What are the functions of the cerebral cortex?
Communication Language processing Sense interpretation e.g. vision, auditory Understanding Memory Voluntary movement (motor processing) Conscious behaviour
What is the cerebral correct composed of?
Grey matter Neuronal cell bodies Dendrites Unmyelinated axons Glia Blood vessels
What three functional areas are contained in the cerebral cortex?
- Motor areas
Control voluntary motor function - Sensory areas
Provide conscious awareness of sensation - Association areas
Act to integrate information for purposeful function e.g. walking
But the brain works as a whole, global integration
What hemisphere is responsible for which side of the human body?
Each hemisphere is responsible for the function of the opposite side of the human body I.e. the right hemisphere governs the left side of the human body
Where is the primary motor cortex located and what does it consist of?
Located in the frontal lobe
Consists of large neutrons called pyramidal cells
Large scones that project down the spinal cord to control skeletal muscle movement. Termed the corticospinal tract
What are the three parts of the motor area of the cerebral cortex?
Premotor cortex
Located in the frontal lobe
Controls learned motor skills e.g. playing a musical instrument
Broca’s area
Located in the frontal lobe anterior to premotor cortex
Involved in co-ordinating speech muscles e.g. tongue
Frontal eye field
Controls eye movement
What is the sensory area of the cerebral cortex?
Somatosensory cortex
Integrated all sensory input for example input from skin (pressure and temperature sensors), vision, olfactory (smell), gustatory (taste) and auditory (sound) information
What is the association area of the cerebral cortex?
The parts of the brain that are not primarily involved in specific functions.
Regions of the cerebral cortex that integrate information from other cortical areas and provide a level of consciousness
This is one of the most complex roles played by the brain
What is cerebral Dominance determined by?
Language dominance
What does ambidexterity mean?
Co-dominance of both hemispheres
What is dyslexia
Lack of cerebral dominance. This does not affect intelligence
What is the diencephalon
Central core of the brain
Surrounded by the cerebral cortex
Consists of three structures:
Thalamus
Hypothalamus
Epithalamus
What is the thalamus
Contains many nuclei that relay information to other regions of the brain e.g. vision and auditory relay centres
It acts as an editing centre And provides direction of motor information
What is the hypothalamus?
Major homeostatic processor and regulator
Autonomic control centre: regulates involuntary nervous system e.g. blood pressure and respiratory rate
Centre for emotional response and behaviour e.g. pain, fear, rage
Body temperature regulation, sweating and shivering responses
Regulation of food intake
Regulation of water balance and thirst
Regulation of the sleep wake cycle
Control of endocrine functions
What is the epithalamus?
Poorly understood area of the brain
Appears to play a role in the sleep wake cycle along with the hypothalamus
Regulates melatonin levels via the pineal gland
What does the brain stem consist of?
Midbrain
Pons
Medulla Oblongata
Describe the position and function of the midbrain
Above the pons
Holds up the cerebellum
Co-ordinates head and eye movement in response to visual stimuli e.g. following an object
Sound reflexes e.g. turning your head when you hear your name
Contains the substantia nigra which plays an important role in reward and movement and is effected in patients with Parkinson’s disease
What is the function of the pons?
Integrates information from the motor cortex and cerebellum (balance)
A pneumotaxic centre- regulation of respiration together with the medulla
What is the medulla oblingata?
Forms the cavity of the fourth ventricle
Autonomic reflex centre involved in maintaining body homeostasis
The medulla oblongata is the centre for what responses?
Cardiovascular centre:
Adjusts the force and rate of heart contraction
Regulates blood pressure by vasodilation/vasoconstriction
Respiratory centre:
Rate and depth of breathing
Maintain respiratory rhythm with pons
Other centres:
Regulates reflexes such as; vomiting, hiccupping, swallowing coughing, sneezing
What is the cerebellum?
Accounts for 11% of the brains mass
Integrates information from the cerebral motor cortex, proprioceptors throughout the body, visual and equilibrium pathways
Proprioceptors: Receptors sending information about muscle tension, tendon and joint position
Acts to maintain posture and estimate force to ensure smooth, co-ordination movement
Ultimately, the cerebellum sends orders to the motor cortex to fine tune movement
Define proprioceptors
Receptors sending information about muscle tension, tendon and joint position
What are the three main protectors of the brain?
The skull (cranium) and its many layers
Cerebrospinal fluid
The blood brain barrier
What are the three protective layers within the cranium?
Dura matter
Thick tough membrane underneath the skull
Arachnoid matter
Thin membrane, projecting to the pia matter through the subarachnoid space
Pia matter: envelopes the contours of the brain suface and dips into the sulci
What is cerebrospinal fluid and what is its function
Cerebrospinal fluid surrounds the entire brain and plays an important role in maintain a constant intracerebral chemical environment
Helps protect the brain form mechanical damage by reducing the effect of impact damage experienced by the head
CSF is secrete by the choroid plexus with is found in the lateral ventricles
The ventricular volume is around 75ml
Describe the route of blood supply to the brain
The blood brain barrier:
The blood brain barrier is both a physical barter and a system of cellular transportation mechanisms
It maintains homeostasis by restricting the entrances of potentially harmful chemicals from the blood whilst still allowing the entrance of essential nutrients
Lipid soluble molecules such as ethanol and caffeine are able to penetrate through the barrier relatively easily via the lipid membranes of the cells. In contrast, water soluble molecules such as sodium and potassium ions are unable to transverse the barrier without the use of a specialised carrier - mediated transport mechanisms
What are the two major roles of the peripheral nervous system?
To send inflation about the environment to the brain
To transmit information to the effector organs of the human body
What are sensory receptors and how are they classified?
They respond to changes in their environment
Environmental changes are called stimuli
There are three basic ways to classify sensory receptors:
1: by their location in the body
2: by the type of stimulus they detect
3: by the relative complexity of their structure
Discuss how sensory receptors are classified by location:
Exteroceptors:
Sensitive to stimuli from outside of the body e..g touch, pressure, pain and temperature receptors in skin
Interceptors (visceroceptors)
Sensitive to stimuli from within the body
E.g. chemical receptors, tissue stretch receptors and temperature (internal)
Proprioceptors:
Respond to internal stimuli
Location is much more restricted that interceptors
Located in skeletal muscle, tendons, joints, ligaments and connective tissue coverings of bones and muscles
Constantly inform the brain of our movements and positions by the degree of stretch of the organs they occupy
How are sensory receptors classified by stimulus type detection?
Mechanoreceptors:
Generate nerve impulses when they, or adjacent tissues are deformed by mechanical forces e.g. touch, pressure (including blood pressure) vibrations and stretch
Thermoreceptors: sensitive to temperature changes
Photoreceptors: retinal photoreceptors
Chemoreceptors: respond to chemical changes
Nociceptors: respond to damaging stimuli that result in pain
How are sensory receptors classified by structural complexity?
Free dendritic endings:
Sensory neutrons
Innervate tissue
Form merkel discs that attach to deep layers of the skin and function as light touch receptors
Root hair plexus Ed wrap around hair roots and function as light touch receptors
Encapsulated dendritic endings:
Dendritic endings are enclosed in connective tissue to form a capsule like structure
Virtually all encapsulated receptors are mechanoreceptors
Meissners corpuscles: pressure sensors on hairless skin e.g. lips and fingertips
Krauses end bulbs: sensors on connective tissue
Pacinian corpuscles: sensors on skin, tendons and ligaments
Muscle spindles: sensors within skeletal muscle
Golgi tendon organs: sensors in tendons
What is meissners corpuscles:
Pressure sensors on hairless skin e.g. lips and fingertips
What are krauses end bulbs?
Sensors on connective tissue
What are pacinian corpuscles?
Sensors on skin, tendons and ligaments
What are golgi tendon organs?
Sensors in tendons
What do uncapsulated receptors in the skin detect?
Pain and movement
What do encapsulated receptors in the skin detect?
Pressure and temperate
What are sensor receptor potentials?
Stimuli acting on receptors are converted into electrical signals, by these reports, that the brain can understand
Receptor potentials are generated in graded stages
These receptors are capable of relating the intensity of a stimulus to electrical output e.g. depolarisation
Basically, the greater the stimulus, the greater the graded depolarisation event
These receptors also show adaptation
What is the spinal column and describe the structure
The route of sensory transmission to the brain
The route of reflex arc processing/ connections
Structure: Made up of vertebrae that can be divided up into the following regions: - cervical - Thoracic - lumbar - sacral
What is the functions of the spinal column?
To provide protection from spinal cord and peripheral nerves
To provide support for the upper torso and skull
To provide and integration channel for all nerves entering/ leaving the central nervous system
Relaying information to and form the brain to peripheral organs
To provide flexible motion
What is the spinal cord?
Lies encased within the spinal column
Bundles of nerves relaying information to and from the brain
What is reflex activity?
Involuntary response initiated by the stimulus
A reflex response can be protective or homeostatic, however it is there to maintain body integrity andc function
A reflex tends to occur through the spinal cord without the involvement of the brain
List the components of a reflex arc?
Receptor: site of stimulus action
Sensory neuron: transmits affront impulses to the CNS
Integration centre: within the CNS, can be a single interneuron or a network of neural connections
Motor neuron: impulses from the CNS to the effector organ
Effector: muscle fibre or gland that responds to the stimulus
Draw and label a simple reflex arc
See lecture slides
What are muscle spindles?
Located within skeletal muscle
Act as stretch receptors
Respond to increases/decreases in muscle contraction
What is the anatomy of muscle spindles?
Intramural fibres: acts as the receptive surface of the spindle
These fibres are wrapped with two types of sensory fibres:
Primary fibres: respond to the rate and amount of stretch
Secondary fibres: respond to the degree of stretch
Gamma fibres: cause the intrafusal fibres to contract (small contractions only)
Alpha fibres: cause the gross contraction of muscle
What are intrafusal fibres?
Intrafusal fibres: acts as the receptive surface of the spindle
These fibres are wrapped with two types of sensory fibres:
Primary fibres: respond to the rate and amount of stretch
Secondary fibres: respond to the degree of stretch
What are gamma fibres?
Cause the intrafusal fibres to contract (small contractions only)
What are alpha fibres?
They cause the gross conduction of the muscle
What does muscle spindles in recruitment mean?
Muscles spindles act to recruit muscle fibres during muscle contraction
For example: when lifting a heavy object, initially your muscles will estimate the weight (via the brain),however if the object is heavier than anticipated, the muscle spindles will stretch on limiting and cause recruitment of muscle fibres i.e. to allow you to apply more force in lifting
What is the stretch reflex?
Golgi tendon organ:
Located at the end of the skeletal muscle at site of bone attachment
Responds to stretch: mechanoreceptors
Proprioceptors
A tap on the patellar tendon induces a stretch reflex i.e. the golgi tendon organ is stretched
This then sends signals to the CNS via afferent sensory neurons
Via interneuronal pathways the extensor muscle is excited whilst the flexor muscle is inhibited through efferent innervations
Outline the roles/ organisation of the peripheral nervous system
See lecture notes
Describe the location classification used fro sensory receptors
See lecture notes
Describe the stimulus detection classification used for sensory receptors
See lecture notes
Describe the structural complexity classification used fort the sensory receptors
See lecture notes
Describe the structure organisation and function of the spinal cord
See lecture notes
Draw a labelled diagram of a spinal cord cross section
See lecture notes
Outline the components of a reflex arc
See lecture notes
Describe the anatomy of muscle spindles and their role in muscle fibre recruitment
See lecture notes
Describe the stretch reflex
See lecture notes
Describe the location of the human brain
See lecture notes
Label a diagram of the major regions of the brain
See lecture notes
Outline the major composition and functions associated with the cerebral cortex
See lecture notes
Outline the major functions associated with the diencephalon, to include the thalamus, hypothalamus and epithalamus
See lecture notes
Label a diagram of the anatomical regions that make up the brain stem
See lecture notes
Outline the functions associated with the brain stem
See lecture notes
Outline the functions associated with the cerebellum
See lecture notes
What protecting mechanisms are in place for the Brain?
See lecture notes
Compare the somatic and autonomic nervous system
See lecture notes
What are effectors?
The somatic nervous system stimulates skeletal muscle
The ANS innervates cardiac and smooth muscles and glands
The different physiology off the effector organs accounts for the differences between somatic and autonomic effects on target organs
What are efferent the pathways and ganglia:
Within the somatic nervous system, the cell bodies lie in the CNS and their axons extend to skeletal muscles (monosynaptic)
These axons tend to be:
Thick
Myelinated fibres
They conduct nerve impulses very fast
In the autonomic nervous system:
The motor unit is a two chain neuron
The cell body of the first neuron (preganglionic neuron) resides in the brain or spinal cord
It’s axon synapses with a secondary motor neuron, the postganglionic is neuron is an autonomic ganglion outside the CNS
The postganglionic axon extends to the effector organ
Draw the efferent pathways of the autonomic nervous system
See lecture slides
What are the effects of neurotransmitters?
The somatic motor neutrons release acetylcholine and are always excitatory
The ANS utilised noradrenalin/adrenaline or acetylcholine
Within the ANS the response can either be inhibitory or excitatory depending on the receptors present at the target organ
Draw the neurotransmitters of the somatic and autonomic nervous systems
See lecture notes
Discuss the overlap of somatic and autonomic function
Higher bran centres regulate and co-ordinate both motor and visceral (internal organ) motor activities
The bodies adaptation to the environment involves both skeletal muscle and enhancements to certain visceral organd
Example running; somatic nervous system inducing skeletal muscle contraction within the legs. The ANS increase heart rate and respiratory rate
Both systems work together
What are the divisions of the ANS?
There are two parts to the ANS:
Parasympathetic division: performs maintenance activated and conserves body energy
Sympathetic division: utilised under extreme conditions ‘fight or flight’ response
Innervate the same target organs
However one has an excitatory effect and the other has an inhibitory effect
What does the parasympathetic division do?
Performs maintenance activities and conserves the bodies energy
What does the sympathetic division do?
Utilised under extreme conditions ‘fight or flight’ response
What is the role of the parasympathetic division?
Most active in non-stressful conditions
Acts to conserve energy
The parasympathetic division acts as follows at rest:
Reduces blood pressure
Reduced heart rate
Reduced respiratory rate
Increase rate of digestion (especially following a meal)
Pupillary constriction (reducing retina damage)
What are the signs that the parasympathetic division is at rest
The parasympathetic division acts as follows at rest:
Reduces blood pressure
Reduced heart rate
Reduced respiratory rate
Increase rate of digestion (especially following a meal)
Pupillary constriction (reducing retina damage)
What is the role of the sympathetic division?
Fight or flight response
Active when we are engaged in an excitatory, emergency or life threatening situation
The sympathetic division acts as follows under the above conditions:
Pounding heart
Rapid deep breath
Cold, sweaty skin
Dilated pupils
Changes in Brian waves and electrical conductivity of skin
What are the signs the sympathetic division has been activated?
Pounding heart Rapid deep breath Cold, sweaty skin Dilated pupils Changes in Brian waves and electrical conductivity of skin
Describe and compare the innervations of the ANS divisions e.g. what happens to body systems at sympathetic division and parasympathetic division
See lecture diagram
What sympathetic adjustments occur during exercise?
Visceral organ blood vessels are constricted
Vessels of the heart and skeletal muscles are dilated
This causes blood to be directed mainly to the heart and exercising skeletal muscle
Dilation of the bronchioles to increase ventilation
Temporary reduction in non-essential activity (for exercise) e..g gastrointestinal and urinary tract motility
Discuss the physiology of the ANS
Neurotransmitters:
Acetylcholine (ACh) and noradrenalin/adrenaline are the major neurotransmitters of the ANS
ACh is predominantly utilised by the majority of parasympathetic neurons
Fibres that release ACh are called cholinergic fibres
The sympathetic nervous system utilities both ACH and noradrenalin/ adrenalin (from adrenergic fibres)
All ACh receptors are either:
Nicotine or muscarinic (named after drugs that were first used to discover these receptors)
ACH binding to nicotinic receptors is always stimulatory e..g muscle contraction
ACh binding to muscarinic receptors can be wither excitatory or inhibitory e.g. slows down heart activity whereas increase gastrointestinal tract motility
Show the typical response to stress
See lecture slides
What has been developed to block the inhibitory and excitatory effects of the ANS
Drugs such as atropine and anticholinesterase
What does atropine do?
Dilutes pupils before surgery
What doe santicholinesterase drugs do?
Drugs such as neostigmine act to inhibit the breakdown of ACh. Used in a condition called myasthenia graves where skeletal muscle activity is impaired due to reduced ACh.
Discuss the interactions of the ANS
Antagonistic interactions:
Clearly seen in the fight or flight response
The sympathetic nervous system increases e.g. heart rate, ventilation during a fight or flight response, however afterwards the parasympathetic system reduces these effects
What is sympathetic tone?
E.g. vascular system, where the vessels are constantly in a state of partial constriction
This allows blood pressure to increase rapidly, as these constrictions can provide pulses to further push the blood along
Alpha blockers act to reduce sympathetic tone and decrease blood pressure
What is sympathetic tone?
Reduces the endogenous rate of function of specific organs
E.g. reduces heart rate below its endogenous rhythm. This is also true of the respiratory system
Pharmacological blockers act to increase the parasympathetic tone e.g. increase heart rate
However, the sympathetic nervous system can override the influences of the parasympathetic nervous system
Describe the differences between the somatic and autonomic nervous system:
See lecture notes
Describe the structural organisation of the ANS neuronal pathway
See lecture notes
Outline the roles of the two divisions of the ANS
See lecture notes
List the sympathetic adjustments that occur during exercise
See lecture notes
List the receptors of the ANS and their associated activation neurotransmitters
See lecture notes
Outline the response to a stressful situation on heart rate
See lecture notes
Outline the functions of sympathetic and parasympathetic tone
See lecture notes
Define neurons and glia
The cells from which the nervous system is assembled
Define neurons
Process and transmit information
Include synapses
Found in the whole of the nervous system
~ 100 distinct types
Define neuroglia
Support neurons and modulate neuronal function
Specific types of glia for each part of the nervous system
There are more glia than there are neurons (10:1)
Draw and label the anatomy of a neuron
See lecture notes
Describe the anatomy of neurons
Process and transmit information in the form of nerve impulses
High degree of morphological and functional asymmetry, Neutrites; Receptive dendrites Transmitting axons Synapses
Electrically and chemically excitable
Draw the structures of
A) multipolar interneurons
B) Motor neurons
C) sensory neurons
See lecture notes
Draw the pain withdrawal reflex arc
See lecture notes
Draw the pain withdrawal reflex showing the peripheral nervous system and central nervous system
See lecture notes
What are glial cells
They support neurons and modulate neuronal functions
What do oligodendrocytes and Schwann cells do?
Form the insulating sheaths of axons
What is an oligodendrocyte and where are they found?
One oligodendrocyte can produce myelin sheaths for segments of as many as 30 axons
Found in the central nervous system
What are Schwann cells and where are they found?
One Schwann cell can produce myeloma sheath for only one segment of a single axon
As many as 500 Schwann cells can participate in the myelination of a peripheral axon
Found in the peripheral nervous system
What is the purpose of myelin sheaths?
They allow rapid conduction of electrical signals along the axon
Lack of myelination slows down or prevents the conduction of electrical signals alone the axon
What do astrocytes do?
Participate actively in synaptic transmission
Draw the process of synaptic transmission in the central nervous system
See lecture notes
What are the supporting roles of astrocytes?
Scaffold of the CNS (structural role)
Clear out synapses e.g. excess glutamate can become toxic
Regulate neurotransmitter concentrations:
Uptake of excess glutamate
Convert glutamate to glutamine
Transfer glutamine to neurons, where glutamine is the precursors or glutamate
Nourish neurons:
Lactate as a neuronal energy substrate
Promote the development of synapses
What part of the body are astrocytes active components of?
The blood brain barrier
What are astrocytes endfeet?
Not much of a structural role
Provide nourishment to endothelial cells that form the bbb
Filtering of unwanted and possibly harmful substances
What are microglia
Microglia play an important role in immunological surveillance of the CNS
They are poised to react to foreign invaders of the CNS
What do microglia do at resting state?
They scan the interstitial fluid
When do microglia work in their active state?
Because of signs of inflammation
Presence of bacteria (infection)
What are the functions of microglia?
Phagocytosis: clearing debris
During inflammation;
Secrete cytokines and chemokines that will serve to trigger an immune reaction
Antigen presentation to lymphocytes
What are ependymal cells
They assist with the move of cerebrospinal fluid CSF though the ventricular system
What is the purpose of CSF
It functions as a shock absorber fluid cushion for the brain and the spinal cord
What are ependymal cells
They are a single layer of ciliated cuboidal epithelial cells
They line the ventricular system
Barrier between the CAF and interstitial fluid
Secretion of CSF
How do neurons communicate?
Neurons are excitable cells and communicate via action potentials
A synapse is an anatomically specialised junction between two cells
One single neuron can synapse onto many other post synaptic cells. This is called divergence
Many synapses from different presynaptic neurones can synapse with a single cells which is called convergence
Define synapse
Anatomically specialised junction between two cells
What is divergence
One single neuron can synapse onto many other post synaptic cells
What is convergence
Many synapses from different presynaptic neurons can synapse with a single cell
What is the function of divergence in neuron communication
A mechanism for spreading stimulation to multiple neurons or neuronal pools in the CNS
What is the purpose of convergence in the communication of neurons
A mechanism for providing input to a single neuron from multiple sources
What are the two types of snynapse
Electrical synapse and chemical synapse
What is an electrical synapse
An electrical synapse is a gap junction
Plasma membranes of cells are joined by gap junctions
Local ionic currents flow from one cell to the next through gap junctions
Communication is extremely rapid
What is a chemical synapse
Operates through the release of neurotransmitters
Draw an electrical synapse diagram
see lecture notes
Draw a chemical ‘tripartite’ synapse
See lecture notes
Draw and label a diagram showing the release of neurotransmitters through chemical synapses
See lecture notes
Draw and label a diagram showing the action of drugs pm a chemical synapse
See lecture notes
How can a drug work on chemical synapses?
A drug might:
1) increase leakage of neurotransmitter from vesicles to cytoplasm in the pre-synaptic neuron
2) increase neurotransmitter release into cleft
3) block neurotransmitter release
4) inhibit transmitter synthesis
5) block neurotransmitter reuptake
6) block cleft enzymes that metabolise neurotransmitter
7) bind to receptor on post synaptic membrane
8) inhibit or stimulate second messenger activity in the post synaptic cell
Describe the communication of neurons
Information is carried within neurons and from neurons to their target cells by electrical and chemical signals
Describe the electrical forces between ions
Opposite charged ions attract each other
Charges of the same type repel each other
The electrical force of attraction increases with the quantity of charge
What is the electrical potential of extra cellular and intracellular
The potential difference across the membrane will be ~69mV
Draw and label a cell and show the charges within and outside of the cell and discuss what the membrane potential is
See lecture notes
Positive and negative ions will be on both sides of the neurons membrane
Excess positive charges will be outside of the cell
Excess negative charges will be inside the cell
This is the membrane potential
Draw and label a diagram of the plasma membrane
See lecture notes
Discuss the resting potentials of neurons
An electrical gradient is maintained across the plasma membrane (treated negative charge inside the cell), thus making the cell polarised
The cell also has a concentration gradient I.e. there is a different in the distribution of ions between the inside and outside of a membrane
Discuss the electrical and concentration gradients across the plasma membrane of a typical neuron
Extracellular:
Na+ : 145mM
K+ : 5mM
Cl- : 100mM
Intracuellar: Na+ : 15mM K+ : 150 mM Cl- :7mM OA- :high concentration of organic anions
When a typical neuron is at rest with a voltage across the membrane of ~60mV
What ions are in higher concentration outside of the cell
Na+ and Cl-
What ions are higher in concentration inside of the cell
K+ and OA-
What a typical neuron is at rest, what is the voltage across the membrane
~60mV
What are the basic principles of electrochemical gradients
Forces that could move ions across cell membranes
Net flux of ions across membranes depends on both the concentration gradient and the electrical different = the two driving forces known as electrochemical gradient
Selective ion channels span the lipid bilayer and allow ions to diffuse across the cell membrane
K+ ions will diffused down their concentration gradient: the next flux occurs from high concentration to low concentration
When k+ ions diffuse down their concentration gradient, they are also going towards a positively charged environment. Charges of the same type will repel each other
Draw and label a diagram showing the basic principles of electrochemical gradients
See lecture notes
How is the resting membrane potential maintained
1) inability of most large anions to leave the cell
2) electrogenic nature of Na+/k+ pump maintaining the concentration gradients
3) leak channels, mainly leak k+ channels
What are leak channels
Allow ions to move down their concentration gradient
Na+ enters the cell
K+ leaves the cell
What is the Na+/K+ pump?
3 Na+ out for every 2 K+ in. This generates concentration gradients
What are the two driving forces known as the electrochemical gradient
Electrical gradient: the ions are attracted to the side of the membrane with the opposite charge
Chemical gradient: diffusion force driving ions down their concentration gradient (from high to low concentration)
Describe small and large graded potentials
SMALL transient changes in the membrane potential confined to small region of the plasma membrane:
Provide signalling in short distances
Depolarising
Hyper-polarising
The magnitude of the transient changes in membrane potential can vary:
Dependent on changes in membrane permeability to ions (ligand gated ion channels)
Decreases with distance and time
LARGE changes in the membrane potential of excitable cells only:
Membrane potentials could change from -60 mV to +40mV
Depolarisation
Overshoot
Repolarization
Hyper polarisation
Return to resting membrane potential
Very rapid
Can repeat at variable frequencies however not during the refractory period
Graded potentials can summate
Initiated at the level of dendrites and soma
Temporal summation
Spatial summation
Draw and label a diagram showing large action potentials
See lecture notes
Where are action potentials initiated
Axon hillock which is an all or none event
Depolarisation of action potentials need to…?
Exceed the threshold Potential
Ion channels allow the generation of…
Large, rapid changes in membrane potential
Such as ligand gated channels
Mechanically gated channels
Voltage gated channels - the ones that give the membrane its ability to undergo an action potential
Describe the propagation of action potentials
• Propagation of APs down the axon is the mechanism the nervous system uses to communicate at long distances
• Each AP produces local currents that depolarize the region adjacent to it
• Sequential opening and closing of voltage-gated Na+ and K+ channels along the axon
• Saltatory conduction: APs appear at the Nodes of Ranvier; Low concentration of voltage
gated Na+ channels on myelinated regions
• AP propagation ceases at the end of the axon
What are the three main parts of the brain
Cerebrum, cerebellum and brain stem
What are the four lobes of the brain
Frontal lobe
Parietal lobe
Occipital lobe
Temporal lobe
What is the function of the frontal lobe
Executive functions Thinking Planning Organising and problem solving Emotions Behaviour control Personality
What is the function of the motor cortex?
Movement
What is the function of the sensory cortex
Sensations
What is the function of the parietal lobe?
Perception
Making sense of the world
Arithmetic
Spelling
What is the function of the occipital lobe
Vision
What is the function of the cerebellum
Coordination and balance
What is the function of the temporal lobe
Memory
Understanding
Language
What is the function of the brainstem
Movement Heart rate control Blood pressure regulation Breathing Swallowing Coughing Sneezing Vomiting Sleeping and waking Dreaming
What parts of the brain are exclusively found in the left hemisphere?
Brocas and wernickes areas
What is Broca’s areas used for
Motor and speech
What is wernickes areas used for
Language comprehension
What can brain damage and impaired function occur
Traumatic injuries
Acquired injuries
Give examples of traumatic injuries
Closed head injury: caused by a rapid forward and backward movement and shaking of the brain inside the bony skull
Concussion: causes impairment in brain function. It can be the result of a closed or penetrating head injury
Contusion; bruise of bleeding in the brain that’s due to a blow or jolt to the head
Penetrating injury: brain injury caused by a bullet, knife or sharpe object. Also known as an open head injury
Shaken baby syndrome: excessive shaking of a young child
Give examples of acquired injuries
Anoxic/hypoxic: injury to brain cells due to a lack of oxygen
Cardiac arrest
Respiratory arrest
Suffocation
Brain infections/inflammation: infections such as meningitis
Stroke: caused by loss of blood flow to The brain
Tumour: can include brain cancer or a cancer related illness
Describe an Ischemic stroke and the main causes
The blood supply is stopped because of a blood clot. The reduced blood flow causes brain cells in the area to die from a lack of oxygen.
The main cause is atherosclerosis (plaques) in the walls of the arteries which feed the brain. Account for 85% of stroke cases
What is a haemorrhagic stroke?
The blood vessel is not blocked but it bursts and blood leaks into the soft brain tissue causing major damage
What are the four types of stroke?
Childhood stroke
Ischemic stroke
Haemorrhagic stroke
A transient ischemic attack (TIA)
What is a transient ischemic attack?
Also known as a mini stroke.
This is the same as a stroke except the symptoms last for a short amount of time and no longer than 24 hours. This is because the blockage that stops blood getting to the brain is temporary. The symptoms are the same as a full stroke
What is a childhood stroke?
A childhood stroke may affect any child from 28 weeks old to the age of 18.
Strokes can be associated with existing conditions, most commonly congenital heart disease and sickle cell disease. Other risk factors include infectious disease, trauma to the head or neck, vascular problems and blood disorders
What are risk factors of strokes:
Obesity Lack of exercise Sleep apnea Heavy alcohol use Smoking and drug use Diabetes Cardiovascular disease High cholesterol High blood pressure
What is the main artery that supplies blood to the brain?
The middle cerebral artery which branches off into the anterior cerebral artery and the posterior cerebral artery.
What is the central nervous system composed of?
Brain
Spinal cord
Relay neurons (interneurons)
What is the peripheral nervous system composed of?
Cranial nerves
Spinal nerves
Peripheral nerves
Sensory neurons
Motor neurons
What is the function of the basal ganglia?
Movement
Reward
What is the purpose of the thalamus?
Sensory gateway
What is the purpose of the hippocampus?
Memory
What is the purpose of the amygdala?
Emotion
What is the function of the hypothalamus?
Regulates body temperature
What is a neuron?
The basic unit of structure and function in the nervous system
Cells that conduct impulses
Made up of dendrites, cell body and an axon
What are dendrites?
Branch like extensions that receive impulses and carry them toward the cell body
What is the axon?
Single extension of the neuron that carries impulses away from the cell body
What is the difference between the axon and dendrites?
The axon branches out at the end to send impulses to many different neurons. Dendrites receive impulses from many other axons
What are Neuroglia?
Provide physical support, control nutrient flow and are involved in phagocytosis
What are astrocytes?
Provide physical support, remove debris (phagocytosis) and transport nutrients to neurons
What are microglia?
Defensive cells
Involved in phagocytosis and brain immune function
What do oligodendrocytes do?
They provide physical support and form the myelin sheath around axons in the brain
How does ageing impact the brain?
Gerontogens are factors, including substances that Can accelerate the ageing process.
Possible gerentogens include arsenic found in groundwater, benzene in industrial emissions, ultraviolet radiation in sunlight and the cocktail of 4000 toxic chemicals in tobacco smoke.
Activities may also be included like ingesting excessive calories or suffering psychological stress
How to differentiate between ageing and neurodegenerative disease?
Neurodegenerative disease results in the progressive degeneration and or loss of nerve cells - they are a heterogeneous group of disorders that are characterised by the progressive degeneration of the structure and function of the central or peripheral nervous system. The function is progressively lost
Whereas,
Ageing shrinks nerve cells - the brain undergo use numerous changes that affect memory, motor and sensory functions. The function is affected but it is still there.
List some common neurodegenerative diseases
Alzheimer’s disease Dementia Parkinson’s disease Multiple sclerosis Motor neuron disease Spinal muscular atrophy
What is Alzheimer’s disease and how was it discovered?
The most common type of dementia which affects 850,000 people in the UK.
Dr Alzheimer noticed changes in the brain tissue of a woman who died of an unusual mental illness. Her symptoms included memory loss, language problems and unpredictable behaviour. After she died, the examined her brain and found many abnormal clumps (now called amyloid plaques) and tangled bundles of fibres (now called neurofibrillary).
What part of the brain is affected by Alzheimer’s and what are the early symptoms:
Hippocampus, the function of the hippocampus is to form memories
Early symptoms: problems with memory and language
- losing items such as keys and glasses around the house
Struggle to find the right word in a conversation
Forgetting someone’s name
Forgetting about recent conversations or events
Getting lost in a familiar place or journey
Forgetting appointments or anniversaries
What causes Alzheimer’s?
Researches believe there is not a single cause of Alzheimer’s disease.
However, it can be influence by multiple factors including ache, genetics, lifestyle and environment.
Discuss the differences between early onset and late onset Alzheimer’s.
Early onset AD: genetically inherited (5%)
Occurs in people aged 30 to 60
Mostly inherited, known as familiar AD
Mutations occur in the following genes:
Amyloid precursor protein
Presenilin 1
Presenilin 2
Late onset AD: sporadic (95%)
In most cases, the cause of AD is multi factorial with both genetics and environmental involvement.
Occurs in people over the age of 60
Combination of genetic and environmental factors
Increased risk associated with other genes:
Apoliprotein E
Triggering receptor expressed on myeloid cells 2
Microtubule associated tau protein
What are the two main features of Alzheimer’s disease?
Plaques and neurofibrillary tangles
What is the treatment for Alzheimer’s?
There is currently no treatment for Alzheimer’s but there are medications available to temporarily reduce the symptoms:
Main drugs currently used:
Acetylcholinesterase (AChE) inhibitors e.g. donepezil, galantmaine and rivastigmine
These drugs work by inhibiting the enzyme acetylcholinesterase, which increases the levels of acetylcholine which is the neurotransmitter essential for processing memory and learning.
AChE inhibitors can be prescribed for patients with early or mid stage AD. The latest guidelines do not recommend these medications in later, severe disease stages.
Memantine:
Memantine is a N-methyl-d-aspartate (NMDA) receptor antagonist which blocks the effect of high glutamate levels. This improves mental function and the ability to perform daily activities for some people and can be used for moderate to severe AD.
Memantine is also suitable for patients who cannot tolerate AChE initiations. It can be also be taken by people with severe AD who are already taking an AChE inhibitor.
Antidepressants:
May sometimes be given if depression is suspected as an underlying cause of anxiety.
What is Parkinson’s disease?
Parkinson’s disease is a progressing nervous system disorder that affected movement.
Parkinson’s is the second most common neurodegenerative disorder after Alzheimer’s disease
What did James Parkinson describe Parkinson’s disease as?
It is a condition which causes characteristic paralysis, diminished muscle strength, abnormal postures and resting tremors.
What are the three main symptoms of Parkinson’s disease?
Tremor
Muscle stiffness
Slowness of movement
What are the two types of Parkinson’s disease?
Parkinson’s disease normally affects older people, but 1 in 20 people diagnosed are under 40. The mean age of onset is 55 years old.
Early onset (genetic): a small proportion of PD cases are genetically inherited
Late onset (sporadic). In most cases, PD is sporadic, with both genetic and environmental involvement
What are the risk factors of Parkinson’s?
Environment: Toxic chemicals Herbicides Pesticides Viruses, bacteria Trauma
Lifestyle:
Stress
Sleep
Diet
Genes
What are the main symptoms of Parkinson’s disease?
TRAP
Tremor; shaking, usually starting on one side of the body
Rigidity; stiffness of the limbs, neck or trunk
Akinesia; loss or impairment in power of voluntary movement
Posture and balance
What causes Parkinson’s disease?
Parkinson’s disease is caused by a loss of nerve cells in part of the brain called the substantia nigra. This leads to a reduction in a chemical called dopamine in the brain
Dopamine plays a viral role in regulating the movement of the body. A reduction of dopamine is responsible for many of the symptoms of Parkinson’s disease
What are the key hallmarks of Parkinson’s disease?
Lewy bodies and lewy neutrites are key histopathological hallmarks of PD.
They are spherical cytoplasmic protein aggregates. They contain numerous proteins including alpha-synuclein, Parkin, ubiquitin and neurofilaments
What is the cure for Parkinson’s disease?
There is currently no cure however there are medications available to temporarily reduce the symptoms.
Current treatments can only help symptomatically and have a limited time efficacy.
Medications such as levodopa
Surgical; deep brain stimulation
Draw the pharmacological treatment of Parkinson’s disease
See lecture slides
Wha this Huntington’s disease ?
It is a genetic disorder (autosomal dominant inheritance) characterised by the gradual and progressive loss of neurons, predominantly in the basal ganglia.
HD can impact movement, learning, thinking and emotions
What is the function of the basal ganglia?
It is responsible for voluntary motor control, procedural learning, eye movement and control of behaviour and motivation
What are the symptoms of Huntington’s disease?
Involuntary movements (chorea)
Weight loss
Abnormal gait
Speech and swallowing difficulties
Personally changes
Depression
Aggression
Early onset dementia
Mean onset age 35-55 years old with death occurring 10-20 years from onset. A small percentage of patients (10%) develop symptoms before the age of 20
Is Huntington’s disease a genetic order and what is the likelihood of the disease being passed on?
HD is a dominant autosomal disorder
If a parent has the gene there is a 1 in 2 chance (50%) chance that each of their children will develop the condition.
Affected children can also pass on the condition to their children
There is a 50% chance of each other of their children never developing the condition- unaffected children cannot pass the condition onto their children
What is a treatment for Huntington’s disease?
Tetrabenazine controls chorea
