New Biological Flashcards
The Nervous System
The nervous system is made up of the brain and the spinal cord, whilst the peripheral nervous system (PNS) relays messages from the environment to the CNS, via sensory neurones, and from the CNS to effectors, via motor neurones.
PNS
- The PNS is further subdivided into the autonomic nervous system (which controls involuntary, vital functions of the body, such as maintaining heart rates and breathing rates) and the somatic nervous system (which receives information from sensory receptors belonging to each of the 5 senses, and results in effectors being stimulated by the CNS, via motor neurones).
The Autonomic Nervous System
- The autonomic nervous system is also subdivided into the sympathetic and parasympathetic branches. These branches work as part of an antagonistic pair during the ‘rest and digest’ response, and are crucial in producing the physiological arousal needed to maintain the fight or flight response.
The Endocrine System
- The endocrine system is the main chemical messenger system of the body, where hormones are secreted into the bloodstream from glands, and then are transported towards target cells in the blood, with complementary receptors. The pituitary gland is considered to be the ‘master’ gland because it controls the release of hormones from all other glands in the body. For example, the thyroid releases the hormone thyroxine, which increases heart rate and therefore increases the rate of growth. The adrenal gland releases adrenaline which creates the physiological arousal preceding the fight or flight response, through increasing the activity within the sympathetic branch of the nervous system.
The Fight or Flight response
1.The body senses and becomes aware of a stressor in the environment e.g. the sound of a speeding car.
2.Through sensory receptors and sensory neurones in the PNS, this information is sent to the hypothalamus in the brain which coordinates a response and triggers increased levels of activity in the sympathetic branch of the ANS.
3.Adrenaline is released from the adrenal medulla in the adrenal glands, and is transported to target effectors, via the blood and through the action of the endocrine system.
4. This results in the rectum contracting, saliva production being inhibited and a greater breathing rate. This creates the physiological response needed to sustain the fight or flight response, whose adaptive purpose is to enable us to escape the stressor and so increase the likelihood of our survival.
5. Once the stressor is no longer a threat, as part of an antagonistic pairing, the hypothalamus triggers less activity in the sympathetic branch and more activity in the parasympathetic branch of the ANS. This is also referred to as the rest and digest response, due to the parasympathetic branch decreasing the activity which was originally increased through the action of the sympathetic branch.
Synaptic transmission
Synaptic transmission is a method of neurons communicating with each other relaying information to the CNS across sensory neurons and carrying out responses dictated by the brain through sending information to effectors via motor neurons.
The process of synaptic transmission is as follows:
1.An action potential arrives at the presynaptic membrane, causing depolarisation through the opening of voltage-dependent calcium ion channels, and the consequent influx of calcium ions.
2.The increased concentration of calcium ions within the membrane causes the vesicles, containing neurotransmitter, to fuse with the presynaptic membrane and release their contents into the synaptic cleft through exocytosis.
3. The neurotransmitter diffuses across the synaptic cleft, down a concentration gradient, and binds to complementary receptors on the post-synaptic membrane. This can result in an inhibitory or excitatory effect in the postsynaptic membrane.
4. The resultant action potential will then be transmitted along the axon of the following neuron, resulting in a ‘cascade’ of neurotransmission!
Neurotransmitters
Neurotransmitters can either have an inhibitory or excitatory effect. Inhibitory neurotransmitters (e.g. serotonin) reduce the potential difference across the postsynaptic membrane through the closure of the voltage-dependent sodium ion channels, reducing the likelihood that an action potential will be generated.
Excitatory neurotransmitters
Excitatory neurotransmitters (e.g. dopamine) increase the potential difference across the postsynaptic membrane through triggering the opening of more voltage-dependent sodium ion channels, increasing the likelihood that an action potential will be generated.
Localisation of Function in the Brain
Localisation theory suggests that certain areas of the brain are responsible for certain processes, behaviours and activities.
The motor area
Separated from the auditory area by the central suclus and found in the frontal lobe, this area is involved in regulating and coordinating movements. Lesions or damage in the motor area result in an inability to control voluntary fine motor movements.
The auditory area
An area of the temporal lobe, located on the superior temporal gyrus, which is responsible for processing auditory information and speech. Lesions or damage in the auditory area causes hearing loss, whereas damage to specific parts of the auditory area (Wernicke’s area) results in Wernicke’s aphasia.
The visual area
An area in the occipital lobe which is responsible for processing visual information.
The somatosensory area
An area of the parietal lobe which processes information associated with the senses e.g. touch, heat, pressure etc. “These regions receive neuronal input from specific 1 nuclei of the thalamus that correspond with the handling of sensation along the lines of touch, pain, temperature and limb position”. Lesions in this area result in a loss of ability to denote sensitivity to particular bodily areas.
Wernicke’s Area
Responsible for speech comprehension and located in the temporal lobe (the left temporal lobe for most people). Lesions or damage (e.g. through stroke and trauma) results in Wernicke’s aphasia, which is characterised by the use of nonsensical words (called syllogisms), no awareness of using incorrect words, but no issues with pronunciation and intonation.