The nervous system can be divided into the ❌ and peripheral nervous systems (CNS and PNS, respectively). The CNS consists of the ❌ while the PNS comprises all the ❌.
The brain is housed within the ❌ and protected by the ❌ and bone. It is divided into two ❌ and its outer structure is dominated by the ❌, which can be divided into a number of ❌ areas.
The spinal cord consists of a ❌ of nerve tissue within the vertebrae which has a series of ❌, each with associated ❌ and dorsal ❌.

The cells within the nervous system can be broadly classed as either n❌ or g❌.
❌ are the main signalling cells and have specialised processes, called a❌ and d❌ for this purpose. They are functionally connected to one another by ❌. Signalling across synapses may be e❌ or c❌. The ❌ neuron will ultimately respond with a changed membrane potential called a ❌.
If the combined input of synaptic potentials is sufficient then the neuron will produce an ❌ which differs in a number of ways from the synaptic potential, not least because it is ❌ .
Although the ❌ of action potentials may vary, the speed of ❌ of action potentials is constant along the length of an axon and depends on a number of factors including whether or not it is ❌: myelinated axons conduct action potentials ❌ than unmyelinated axons.
❌ provide support and ❌ to the nervous system. They have ❌ duties, nourishing nervous tissue by regulating the supply of ❌, including oxygen, and also a ❌ role by mopping up debris and buffering ions in the extracellular fluid. They also provide ❌: ❌ in the CNS; ❌ in the PNS.

The ❌, similar to the membrane surrounding other cells, is a highly dynamic structure composed of a ❌ in which are immersed glycolipids, ❌ and other protein molecules.
The neuronal membrane acts as a ❌ separating the internal chemical environment from that outside the neuron.
Some of the ❌, glycoprotein and protein molecules embedded in the cell membrane act as ❌ for ❌.

There are three main transport mechanisms across the neuronal membrane:
◦ passive ❌
◦ transport by ❌
◦ in membrane-bound ❌.
The unequal distributions of K+ and Na+ on the inside and outside of the neuronal membrane produce ❌ and potential ❌.
When these concentration and potential gradients are at an ❌, there is a potential difference (a voltage) across the neuronal membrane of about ❌. This equilibrium or ❌ can be calculated from the Nernst equation (and by the Goldman–Hodgkin–Katz equation if membrane permeability is considered).

When the neuronal membrane is sufficiently ❌ to a critical threshold value, an ‘all-or-nothing’ action potential is generated at the ❌ and transmitted along its axon to the ❌.
An action potential has ❌ distinct phases – depolarisation, repolarisation and ❌ – which involve the highly ordered movement of ❌ across the neuronal membrane through ❌.
Action potentials travel faster in ❌ and those with a larger ❌. Temperature may also affect conduction speed.

The passage of a signal across an ❌ can be in either direction (❌) and there is no ❌. By contrast, a ❌ is ❌ (goes one way only) and subject to a synaptic delay caused by the need to release the ❌, have it travel across the ❌ and have its affect on the ❌.

The release of ❌ from a chemical synapse requires that there is first an influx of ❌ across the ❌.
After release, the neurotransmitter binds to ❌ on the ❌ and, directly or indirectly, this leads to the opening of ❌ so that ions can cross the membrane.

Depending on the type of ❌ opened and the specific ❌ that can cross the ❌, the membrane will be ❌ (EPSP) or ❌ (IPSP). The neurotransmitter is ❌ from the ❌.
Neurons ❌ afferent inputs using ❌ and temporal ❌.

There is a great variety of ❌ but they all have specific ❌ and are capable of generating a ❌ which can affect the firing of ❌ sending sensory information to the ❌. In some cases, the afferent neuron and receptor cell are the same.
Alternatively, where the receptor cell is not equipped to produce an action potential, it will ❌ with an afferent ❌ capable of doing so.

Sensory signals reach the CNS via the ❌ and cranial ❌.
Once in the CNS, the majority of information crosses the ❌ to be processed on the ❌ side of the brain.

The majority of information travels to the ❌ for processing via the ❌ which acts as a filter for ❌.
The architecture of the cortex includes both ❌ layers and vertical ❌. These columns are functional units where incoming ❌ are integrated into information ❌ within the cortex.
There are two main types of ❌ within the cortex: the ❌ cell which projects to other areas and ❌ which remain within the cortex.

Neurons can be combined in a variety of different types of ❌ which can have implications for ❌, as illustrated by ❌.
There are two main theories for understanding ❌: the ❌ line theory and the ❌ theory.

Modern imaging techniques are classified as being structural or functional.
❌ imaging techniques (CT, MRI) are essentially static techniques that provide images of the ❌, or anatomy, of different parts of the body.
❌ brain imaging techniques aim to map sensory, motor and cognitive functions to specific regions. In functional imaging, ❌ relates to the smallest distance over which distinct and reliable information relating to brain activity can be established. ❌ relates to the smallest timescale over which functional images can be measured.

There are four main functional brain imaging techniques: ❌ (EEG), ❌ (MEG), ❌ (PET) and ❌ (fMRI).
MEG and EEG are ❌ techniques since they measure, respectively, ❌ fields and ❌ currents associated with neuronal activity.
PET and fMRI are ❌ techniques since they measure local changes in the ❌ of the brain, for example those associated with increased ❌, which are taken to correlate with ❌ in the brain.
PET involves a participant being administered a substance that is specifically labelled with a ❌ that decays by positron emission.
A popular fMRI technique is based on ❌: blood oxygenation level­ dependent contrast.

❌ in the order of a few millimetres can be achieved for MEG, PET and fMRI. In PET and fMRI, all parts of the brain are sampled with equal spatial resolution, whereas using MEG spatial resolution degrades for regions ❌ inside the brain. The spatial resolution for ❌ is not well defined.
MEG and EEG recordings can be taken on a ❌ timescale. For ❌, temporal resolution is at best in the order of 40 s, whereas for ❌ it can be reduced to the order of a second.

Diffusion tensor imaging (❌) is a relatively new procedure that is able to chart the probabilistic course and distribution of ❌ in the white matter of the living brain on the basis of the diffusion of ❌ along ❌.

Designing suitable stimulus paradigms is an important part of functional imaging and the choice of ❌ itself can be critical. A common stimulus presentation pattern in PET and fMRI is to use regular periods of ❌ In EEG and MEG studies a single, ❌ strategy is often used.

Neurons in the CNS have a central ❌ containing different ❌. Most neurons have numerous ❌ which radiate outwards from the cell body and can have an abundance of ❌ over their surfaces. A neuron also possesses an ❌ which can transmit electrical signals in the form of ❌. These signals are generated at the ❌. If the axon is ❌ the electrical signals travel via ❌ conduction to the axon ❌ where ❌ are established with other neurons.

The first phase in the production of an action potential is the opening of ❌ which cause ❌ to enter the cell. This initiates a ❌ of the potential difference across the cell membrane from its ❌ of ❌ towards a membrane potential of about +30mV.
During the second phase, ❌ open allowing ❌ to leave the cell. As a result there is a ❌ of the membrane potential back towards its initial negative value.
The loss of K+ together with the ❌ of Na+ channels, causes the potential difference across the membrane to become more negative inside the axon than its initial polarised value - this third phase is called ❌. The situation is reversed by the action of ❌ pumps which gradually return the membrane potential to its resting potential - the time when the neuron is in this state is named the ❌ period.